“Topological Phases and Functionalityof Correlated Electron Systems”(TPFC2019)18th ‒ 20th Feb, 2019
Kashiwanoha Campus Station Satellite,
The University of Tokyo, Kashiwa, Japan1

Scope:For a long time, magnetism has been a central subject in strongly correlated electron systems.
More recently, topology led to a new classification of band insulators, namely topologicalinsulators. Where magnetism and topology meet, we find many intriguing phenomena including
emergent "relativistic" particles and multipolar degrees of freedom. The novel physics also opens
up a promising direction in spintronics and other potentially practical applications. In thisconference, we will explore experimental and theoretical studies on subjects ranging fromfundamental issues in correlated topological phases to their cutting-edge applications tospintronics.

Organizers:
Satoru Nakatsuji

Institute for Solid State Physics, The University of Tokyo

Yoshichika Otani

Institute for Solid State Physics, The University of Tokyo

Masaki Oshikawa

Institute for Solid State Physics, The University of Tokyo

Collin Broholm

Johns Hopkins University

Hisatomo Harima

Kobe University

Shinji Miwa

Institute for Solid State Physics, The University of Tokyo

Hiroki Wadati

Institute for Solid State Physics, The University of Tokyo

Supported by
Institute for Solid State Physics, The University of Tokyo
J-Physics: Physics of Conductive Multipole Systems
Nano Spin Conversion Science
CREST
Johns Hopkins University

2

PROGRAM OF WORKSHOP
Feb. 18 (Mon.)
09:15-10:00

Registration

Opeing (Chair: S. Nakatsuji)
10:00-10:20

Opening announcement, S. Nakatsuji
Opening remarks, H. Mori

Session 1: Topological phases (Chair: L. Balents)
10:20-10:50

10:50-11:20(O18-1) K. L. Wang

Topological Transitions and Chiral Majorana

Univ. of California

Fermion(O18-2) Y. Tokura

Emergent magneto-transport phenomena in

RIKEN Center for Emergent

strongly correlated topological phase

Matter Science (CEMS)
11:20-11:45

11:45-12:10

12:10-14:00(O18-3) T. Tomita

Topological Nature and Anomalous Nernst

ISSP, The Univ. of Tokyo

effect in Magnetic Weyl Metals(O18-4) T. Kondo

Discovery of weak topological insulator state

ISSP, The Univ. of Tokyoin quasi-one-dimensional bismuth iodide

Lunch

Session 2: Dynamics in quantum spin liquids (Chair: C. Broholm)
14:00-14:30(O18-5) L. Balents

Dynamics and transport in quantum magnets

Kavli Inst. of Theoretical
Physics, Univ. of California
14:30-15:00(O18-6) H. Mori

Proton-dynamics Coupled Quantum Spin

ISSP, The Univ. of Tokyo

Liquid State and Magnetic Switching in
Organic Mott System3

15:00-15:30(O18-7) N. Drichko

The quantum dipole liquid in triangular lattice

Johns Hopkins Univ.

molecular Mott insulators and its relevance toa spin liquid

15:30-15:55

15:55-16:25(O18-8) Y. Tada

Theory of proton-driven quantum spin-dipole

ISSP, The Univ. of Tokyo

liquidCoffee break

Session 3: Metal spintronics (Chair: T. Jungwirth)
16:25-16:55(O18-9) S. Yuasa

Voltage control of magnetic anisotropy andNatl. Inst. of Advanced Industrial

its application to voltage-torque MRAM

Science and Technology
16:55-17:20(O18-10) S. Miwa

Electric-field-inducedchangeof

ISSP, The Univ. of Tokyo

perpendicularanisotropyatmagnetic

metal/dielectric interface
17:20-17:45(O18-11) K. Yamamoto

Ultrafast demagnetization in Pt-containing

ISSP, The Univ. of Tokyo

ferromagnetic thin films probed by x-ray freeelectron laser

Feb. 19 (Tue.)
Session 4: Topological spintronics (Chair: YC. Otani)
09:00-09:30(O19-1) A. H. MacDonald

Magic Angle Twisted Bilayer Graphene

Physics Dept., Univ. of Texas atAustin
09:30-10:00(O19-2) R. Arita

Anomalous transverse transport and domain

Dept. of Applied Physics, Thewall motion in non-collinear antiferromagnets

Univ. of Tokyo
10:00-10:30

Coffee break4

Session 5: Antiferromagnetic spintronics (Chair: A. H. MacDonald)
10:30-11:00(O19-3) T. Jungwirth

Crystalsymmetries

andInst. of Physics, Academy ofphenomena in antiferromagnets

transport

Sciences of the Czech Republic
11:00-11:25(O19-4) T. Higo

Large time-reversal-odd responses in the

ISSP, The Univ. of Tokyo

Weyl antiferromagnet Mn3Sn bulk and thinfilm for antiferromagnetic spintronics

11:25-11:50(O19-5) K. Kondou

Observation of magnetic spin Hall effect and

RIKEN Center for Emergent

magnetic inverse spin Hall effect in a chiralMatter Science (CEMS)

antiferromagnet Mn3Sn

Poster session (Chair: S. Miwa)
11:50-13:50

Photo
Poster preview

13:50-15:50

Poster presentation

15:50-16:20

Coffee break(Lunch box provided),

Session 6: Excitations in quantum spin liquids (Chair: O. Tchernyshyov)
16:20-16:50

16:50-17:15

17:15-17:40(O19-6) Y. Matsuda

Majorana fermions and half-integer thermal

Dept. of Physics, Kyoto Univ.

quantum Hall effect in a quantum spin liquid(O19-7) M. Yamashita

Spin Thermal Hall Conductivity of a Kagomé

ISSP, The Univ. of Tokyo

Antiferromagnet(O19-8) D. Hirai

Gapless

ISSP, The Univ. of Tokyo

triangular lattice antiferromagnet A3ReO5Cl2

spin(A = Ca, Sr, Ba)
18:30-

Conference dinner (MC: H. Wadati)

5liquidintheanisotropic

Feb. 20 (Wed.)
Session 7: Topological and chiral magnets (Chair: N. P. Armitage)
09:00-09:30(O20-1) N. Nagaosa

Nonreciprocal transport in quantum materials

RIKEN Center for Emergent
Matter Science (CEMS)
09:30-10:00(O20-2) K. Kaneko

Skyrmion lattice in f-electron magnet EuPtSi

Materials Sciences ResearchCenter, Japan Atomic Energy
Agency10:00-10:25

10:25-10:55(O20-3) T. Sakakibara

Magnetization of the skyrmion lattice phase

ISSP, The Univ. of Tokyoand field-induced tricritical point in EuPtSi

Coffee break

Session 8: Multipolar Kondo systems (Chair: H. Harima)
10:55-11:25(O20-4) Y. B. Kim

Theory of Multipolar Order and Multipolar

Dept. of Physics, Univ. of

Kondo EffectToronto11:25-11:55

11:55-14:00(O20-5) M. Takigawa

Field-induced switching of ferro-quadrupole

ISSP, The Univ. of Tokyo

order parameters in PrTi2Al20

Lunch

Session 9: Quantum criticality and superconductivity (Chair: Y. Matsuda)
14:00-14:30

14:30-15:00(O20-6) C. Broholm

Incommensurate

Johns Hopkins Univ.

fermion systems(O20-7) C. Hicks

Evaluation of chiral superconductivity in

Max Planck Inst. for Chemical

Sr2RuO4

Physics of Solids

6

magnetism

in

heavy

15:00-15:30

Coffee break

Session 10: Spin currents and dynamics (Chair: Y. B. Kim)
15:30-16:00(O20-8) E. Saitoh

Spin current in quantum spin liquids andDept. of Applied Physics, The

superconductions

Univ. of Tokyo
16:00-16:30(O20-9) O. Tchernyshyov

Mapping the XY ferromagnet in d=2+1 onto

Inst. for Quantum Matter andelectrodynamics

Dept. of Physics and Astronomy,
Johns Hopkins Univ.
16:30-17:00(O20-10) N. P. Armitage

Shining (THz) light on quantum magnetic

ISSP, The Univ. of Tokyosystems

Closing (Chair: M. Oshikawa)
17:00-

Poster awards
Closing remarks, M. Oshikawa

7

List of Poster Presentations (Feb. 19, 13:50-15:50)
P01

M. Akazawa
ISSP, The Univ. of Tokyo
Thermal transport properties of S = 1/2 kagome frustrated Cd-kapellasite

P02

Y. Asaka
Dept. Eng. Sci., Univ. of Electro-communications
Spin-density-wave transition and Seebeck coefficient in quasi-one-dimensionalorganic conductors

P03

Y. Awashima
Dept. of Eng. Sci., Univ. of Electro-Communications
Theoretical study on magnetoresistance of SrTiO3

P04

C. Bareille

ISSP, The Univ. of Tokyo

Strongly anisotropic high temperature Fermi surface of the Kondo semimetal CeNiSnrevealed by ARPES
P05

P06

P07

H. Chono
Dept. of Physics, Kyoto Univ.
Laser-induced topological phase transitions indichalcogenides

bilayertransition

metal

A. Daido
Kyoto Univ.
Local Magnetic Quadrupole Moments in Insulators
T. Fujii
Graduate School of Material Science, Univ. of Hyogo
P-NMR study of pressure induced semiconductor – semimetal transition in Black
Phosphorus
31

P08

Y. Fujishiro
Dept. of Applied Physics, The Univ. of Tokyo
Transitions of topological spin textures between skyrmion- and hedgehog-latticestates in cubic chiral magnets MnSi1-xGex

P09

H. Fujita
ISSP, The Univ. of Tokyo
Topological lightwaves for optical physics

P10

S. Furukawa
Dept. of Physics, The Univ. of Tokyo
Dzyaloshinskii-Moriya interactions in volborthite: magnetic orders and thermal Hall
effectP11

I. HaseAIST, Japan
Flat-Band Compound as a Possible Candidate of Topological Material

P12

D. Hirai
ISSP, The Univ. of Tokyo
Spin-orbit coupled insulator Ba2MgReO6

8

P13

M. Hirschberger RIKEN Center for Emergent Matter Science
Skyrmion formation in centrosymmetric materials

P14

M. Hosoi
Dept. of Phys., The Univ. of Tokyo
Multipolar DM interaction in 5d electron systems

P15

S. Iimura
Dept. of Phys., Saitama Univ.
Mechanism of superconductivity in Kondo lattice with semi-metallic conduction
bands

P16

Y. Ikeda
Kyoto Univ.
Supercurrent-induced Edelstein effect

P17

A. Ikeda
ISSP, The Univ. of Tokyo
Excitonic condensation in correlated cobaltite LaCoO 3 at ultrahigh magnetic field

P18

M. Ikhlas
ISSP, The Univ. of Tokyo
Magnetic Phases of Non-collinear Antiferromagnet Mn3Sn

P19

H. Ishizuka
Dept. of Applied Physics, The Univ. of Tokyo
Rectification of Spin Current in Magnetic Insulators with Linearly-PolarizedElectromagnetic Waves

P20

T. Isomae
ISSP, The Univ. of TokyoNQR Study of Multipole orders in PrT 2Al20 (T=Ti, V)

P21

Y. IzakiDept. Eng. Sci, U. Electro-Communications
Anomalous Zeeman effect in strongly spin-orbit coupled systems

P22

R. KadonoInst. Mater. Struct. Sci., KEK
Coupled Spin-Charge Fluctuation in the Semimetal Phase of All-In/All-Out
Antiferromagnet Cd2Os2O7

P23

S. Kanasugi
Kyoto Univ.
Spin-orbit-coupled ferroelectric superconductivity and multiorbital effects in doped
SrTiO3

P24

R. Kaneko
Dept. of Applied Physics, Univ. of Tokyo
Enhanced Thermopower in Hole-doped Pyrochlore Iridates with Quadratic Band
Touching

P25

R. Kaneko
ISSP, The Univ. of Tokyo
Assessing the numerical accuracy of tensor-network representation of the Kitaev
spin liquid

9

P26

M. Kawano
Basic Science, Univ. of Tokyo
Rashba-Dresselhaus effect in magnetic insulators

P27

S. Kittaka
ISSP, Univ. of Tokyo
Field-orientation effect on the hidden-order transition in URu2Si2

P28

A. Kobayashi
ISSP
Synthesis and magnetic transport properties of antiferromagnet Mn 3Ge, Mn3Sn thin
films

P29

H. Kondo
Dept. of Physics, The Univ. of Tokyo
Z2 topological invariant for magnon spin Hall systems

P30

H. Masuda
Dept. of Applied Physics, The Univ. of Tokyo
Impact of antiferromagnetic order on Landau level splitting of quasi-two-dimensional
Dirac fermions in EuMnBi2

P31

K. Matsubayashi The Univ. of Electro-Communications
Pressure-tuning of the interplay between ferroquadrupole
superconductivity in PrTi2Al20

order

P32

T. Matsuda
ISSP, The Univ. of Tokyo
Terahertz anomalous Hall effect in Weyl antiferromagnet Mn3Sn thin film

P33

A. H. Mayo
Depart. of Applied Physics, The Univ. of Tokyo
Band-tuning-induced giant topological Hall effect in magnetic semimetal α-EuP3

P34

T. Chenand

ISSP, The Univ. of Tokyo

Large Topological Responses in the Antiferromagnet Mn3Ge
P35

Y. Michishita
Kyoto Univ.
Non-hermitian properties in f-electron materials

P36

T. Miyamachi
ISSP, The Univ. of Tokyo
Atomic-scale structural and electronic properties of YbB12(001) surfaces

P37

T. Mizoguchi
Dept. of Physics, Univ. of Tsukuba
Majorana edge magnetization in the Kitaev honeycomb model

P38

M. Mogi
Dept. of Appl. Phys., The Univ. of Tokyo
Large anomalous Hall effect in topological insulators with proximitized ferromagnetic
insulators

10

P39

H. Nakamura
ISSP, The Univ. of Tokyo
Topologically Enhanced Anomalous Nernst Effect in Half-Heusler Ferromagnet
CoMnSbP40

T. Nakamura
ISSP, The Univ. of Tokyo
In-plane field and current dependence of the Josephson effect in Nb/InAs/Nbjunctions

P41

J. Nasu
Dept. of Physics, Yokohama Natl. Univ.
Non-equilibrium dynamics by field quench in Kitaev model

P42

R. Noguchi
ISSP, The Univ. of Tokyo
Quasi-1D bismuth halides exhibiting various topological phases investigated by
ARPES

P43

T. Ohtsuki
ISSP, The Univ. of Tokyo
Spontaneous Hall effect in a Luttinger semimetal Pr2Ir2O7 thin film

P44

S. Okumura
Dept. of Applied Physics, The Univ. of Tokyo
Numerical study of nonreciprocal spin current in monoaxial chiral magnets

P45

T. OmiDept. of Advanced Materials Science, The Univ. of Tokyo

Magnetic phase diagram of an orthorhombic Kagomé cobaltite CaBaCo4O7
P46

M. Onizaki
ISSP, The Univ. of Tokyo
Supercurrent on accumulation edges of an InAs quantum well

P47

S. Ono
ISSP, The Univ. of Tokyo
Symmetry indicators for topological superconductors

P48

R. Peters
Kyoto Univ.
Quantum oscillations in topological Kondo insulator

P49

J. Puebla
CEMS-RIKEN
Spin to charge conversion via magnon - phonon coupling

P50

H. Saito
Spintronics Research Center
Spin-dependent diode performance in fully epitaxial magnetic tunnel junctions withrock-salt type ZnO/MgO bilayer tunnel barrier

P51

A. Sakai
ISSP, The Univ. of Tokyo
Giant anomalous Nernst effect at room temperature

P52

in Co2MnGa

N. Sakamoto
Dept. of Physics, Graduate School of Science, Kyoto Univ.
Chirality inversion and thermal Hall effect in Weyl superconducting state of URu 2Si2

11

P53

R. Sakano
ISSP, The Univ. of Tokyo
Spin current correlation in a three terminal quantum dot

P54

S. Sakuragi
ISSP, The Univ. of Tokyo
Observation of magnetically combined two-dimensional electronic states in a layered
antiferromagnet EuSn2As2

P55

R. Sasaki
Basic Science, The Univ. of Tokyo
Surface acoustic wave on natural and artificial multiferroics.

P56

T. Shimizu
ISSP, The Univ. of Tokyo
Control of electron spin through quantum Hall edge-spin entanglement

P57

N. Sogabe
ISSP, The Univ. of Tokyo
Quadrupolar Kondo Effect in Magnetoresistance of Non-magnetic Γ3 System
PrV2Al20

P58

D. Takagi
Dept. of App. Phys, Nagoya Univ.
Theory of proximity effect in Rashba nanowire junction

P59

T. Takashiro
Dept. of Phys., Univ. of Tokyo
Fabrication and Evaluation of Magnetic Topological Insulator Heterostructure MnTe/(Bi1-x,Sbx) 2Te3

P60

H. Takeda
ISSP, The Univ. of Tokyo
Pressure induced phase transition on a frustrated square lattice spin system
RbMoOPO4Cl

P61

K. Takubo
ISSP, The Univ. of Tokyo
Observation of collective phonon mode in quantum spin-orbital liquid Ba3CuSb2O9
using time-resolved resonant x-ray scattering

P62

K. Tanaka
Dept. of Basic Science, Univ. of Tokyo
Realization of spin nematic phases in antiferromagnetic dimer dumbbell models on
two-dimensional lattices

P63

N. Tang
ISSP, The Univ. of Tokyo
Metamagnetism, Criticality and Dynamics in the Quantum Spin Ice Pr 2Zr2O7

P64

Y. Tomioka
AIST
Superconductivity near a ferroelectric quantum critical point in La-doped SrTiO3

P65

R. Toshio
Dept. of Physics, Kyoto Univ.
Applications of Electron Hydrodynamics to Nonlocal and Nonlinear Optical Effects

P66

K. UedaDept. of Applied Physics, The Univ. of Tokyo
Spontaneous Hall effect in all-in all-out Weyl semimetal of pyrochlore iridate

12

P67

R. Yamada
Dept. of Applied Physics, The Univ. of Tokyo
Strong-correlation induced highly mobile electrons in Dirac semimetal of perovskite
CaIrO3

P68

K. Yamamoto
Dept. of Physics, Kyoto Univ.
Fate of loss-induced superconductivity studied by non-Hermitian mean field theory

P69

T. Yamamoto
ISSP, The Univ. of Tokyo
Quantum critical phenomena in heat transport in the subohmic spin-boson system

P70

H. Yasuoka
Max Plank Institiute, CPfS
Local magnetic excitations in Weyl semi-metals explored by NMR and NQR
spectroscopy.

P71

T. Yokouchi
CEMS, RIKEN
Creation of skyrmions by surface acoustic waves

P72

T. Yoshida
Univ. of Tsukuba
Symmetry-protection of exceptional points for correlated systems in equilibrium

P73

Y. Zhang
ISSP, The Univ. of Tokyo
Investigation of Ir Magnetism in LaMnO3/SrIrO3 Superlattices by Hard X-ray
Magnetic Circular Dichroism

P74

Z. Zhu
ISSP, The Univ. of Tokyo
Comparison of Spin Hall Angles for Epitaxial and Polycrystalline Platinum Thin Films

13

Abstracts of Workshop

14O18-1Topological Transitions and Chiral Majorana Fermion
Kang L. Wang
Departments of Electrical & Computer Engineering, Materials Science & Engineering,
Physics and Astronomy; University of California, Los Angeles, CA 90095, USA
E: wang@seas.ucla.edu; P: 310-825-1609
Energy dissipation has become the major challenge for today’s electronics and computer.

Recent advances of physics incorporating topology with spintronics have revealed new
physics and at the same time made possible many device possibilities. Topologicaltransitions have also been used to demonstrate dissipation-less quantum anomalous Hall inmagnetic doped topological insulator and to control spin texture. In particular, topologicalmaterial heterostructures composed of, e.g., TI and antiferromagnets (AFM) or
superconductors are shown to offer interesting new physics. In this talk, some of these physics
and potentials will be discussed. Specifically, AFM/TI heterostructures are shown to give rise
to a marked increase in magnetic orders, e.g., exchange coupling with three times ofenhancement in the Curie temperature of a magnetic doped TI. These topological transitions at
the interfaces of the TI/AFM heterostructure can be controlled by applying a small magnetic
field. The edge state of the quantum anomalous Hall using a magnetic doped topologicalinsulator has been demonstrated to have millimeter coherent transport lengths. For theheterostructure consisting of a QAH edge state interfaced with a superconductor, new phase
topological phase transitions can also occur and a topological superconductor phase ispredicted. For such heterostructure, by reducing three dimensional systems to two dimensions
at the interface, chiral Majorana can be hosted. Majorana was proposed in 1937 by Ettore
Majorana as a particle being its antiparticle. Since its inception, Majorana has been underintensive pursuit both theoretically and in experiments. In the heterostructure consisting of a
QAH insulator and a superconductor, our recent experimental results showed a half-integer anda two-integer of quantized conduction plateaus (0.5 e2/h and 2 e2/h), which give firm signaturesof the elusive Majorana fermion for the first time in 80 years. A recent report of different
systems using an InSb nanowire interfaced with a superconductor confirmed a similar twoquantized plateau. The contrast of ours results with the more recent confirmation using the
InSb nanowire with a superconductor mentioned above will also be discussed [2]. Using
Majorana particles as topological qubits, topological quantum computer may be realized. The
findings offer a new direction for robust topological quantum computing to mitigate the decoherence challenge. Our finding offers a potential for constructing robust topologicalquantum computing to mitigate the challenge of decoherence of today’s approaches inquantum computer.
[1]. Qinglin He, .. Kang L Wang, Science, V.357, Issue 6348, pp. 294-299 (21 July, 2017);[2]. Hao Zhang, … Leo Kouvenhoven, Nature V.556, pages 74–79 (05 April 2018)*The work was in part supported by ERFC-SHINES, MURI-ARO, TANMS, and
FAME

15

O18-2
Emergent magneto-transport phenomena in strongly
correlated topological phase
Yoshinori Tokura 1, 2
1
RIKEN Center for Emergent Matter Science (CEMS), Japan2
Department of Applied Physics, The University of Tokyo, Japan
Berry curvature arising from the Weyl fermions and/or the real-space scalar spinchirality can give rise to the action of effective magnetic field on the conduction
electrons and hence produce the topological Hall effect. Furthermore, their temporal
dynamics can also cause versatile emergent phenomena, including nonreciprocaltransport, enhanced carrier scattering, thermoelectric effect, etc. Here, taking theexamples of cubic chiral magnets, frustrated triangular- or Kagome-lattice magnets andmagnetic topological insulators, we report the experimental attempts to design andmaximize the emergent magnetic-field effects with possible applications to spintronic
functions.

[1] A. Author, B. Second and C. Third, Phys. Rev. B 100, 012345 (2019).
[2] http://tpfc.issp.u-tokyo.ac.jp/registration.htm

16O18-3Topological Nature and Anomalous Nernst effect inMagnetic Weyl Metals
T. Tomita1, T. Chen1, M. Ikhlas1, T. Koretsune2, R. Arita3, and S. Nakatsuji1
1
Institute for Solid State Physics, The University of Tokyo, Japan.
2
Department of Physics, The University of Tokyo, Japan.
3
Department of Physics, Tohoku University, Japan.
Antiferromagnets Mn3X (X = Sn, Ge) are found to exhibit a large anomalous Hall effect, evenat room temperature and far above, although having vanishingly small magnetization [1,2].
Usually, this anomalous Hall effect is known to be proportional to magnetization and thus has
been observed only in ferromagnets. The spontaneous Hall resistivity indicates that the large
fictitious field equivalent to a few hundred T must exist in the momentum space. Recent DFT
calculation predicts that the large fictitious field may well come from a significantly enhanced
Berry curvature associated with the formation of Weyl points nearby the Fermi energy EF [3].
Recent theoretical study of magnetic space group have also clarified the ferroic-order ofmagnetic octupoles in chiral non-collinear Mn3X is sufficient to induce a non-zero net Berrycurvature [4].
Here, we report a striking discovery of a large spontaneous Nernst effect of ~ 0.35 μV/K in
Mn3Sn at room temperature and ~ 0.6 μV/K at low temperatures. The Nernst signals are foundmore than 100 times larger than what would be expected based on the magnetization [5].
Besides, we found strong experimental evidence of the Weyl fermions in Mn 3Sn, namely, thatthe band structure is found consistent with DFT by ARPES and the chiral anomaly is clarified
in the magnetotransport measurements. Thus, our experiments demonstrate that the large
anomalous Hall and Nernst signals arise from the Berry curvature associated with the Weyl
points near the EF [6]. In our talk, we also inform the anomalous Nernst effect of Mn3Ge anddiscuss the topological nature of Weyl magnets by comparing Mn3Ge with Mn3Sn.
[1] S. Nakatsuji, N. Kiyohara, and T. Higo, Nature 527, 212-215 (2015).
[2] N. Kiyohara, T. Tomita, and S. Nakatsuji, Phys. Rev. Applied 5, 064009 (2016).
[3] H. Yang, Y. Sun, Y. Zhang, W-J. Shi, S. S. P. Parkin, and B. Yan, New J. Phys. 19, 015008(2017).
[4] M.-T. Suzuki, T. Koretsune, M. Ochi, and R. Arita Phys. Rev. B 95, 094406 (2018).
[5] M. Ikhlas, T. Tomita, T. Koretsune, M. –T. Suzuki, D. Nishio-Hamane, R. Arita, Y. Otani,and S. Nakatsuji. Nature Physics 13, 1085-1090 (2017).
[6] K. Kuroda, T. Tomita, M.-T. Suzuki, C. Bareille, A. A. Nugroho, P. Goswami, M. Ochi, M.
Ikhlas, M. Nakayama, S. Akebi, R. Noguchi, R. Ishii, N. Inami, K. Ono, H. Kumigashira,A. Varykhalov, T. Muro, T. Koretsune, R. Arita, S. Shin, T. Kondo, and S. Nakatsuji,
Nature Materials 16, 1090-1095 (2017).

17

O18-4
Discovery of weak topological insulator statein quasi-one-dimensional bismuth iodide
Takeshi Kondo
Institute for Solid State Physics, The University of Tokyo, JapanThe major breakthroughs in the understanding of topological materials over the past decadewere all triggered by the discovery of the Z2 topological insulator (TI). In three dimensions (3D),
the TI is classified as either “strong” or “weak”, and experimental confirmations of the strong
topological insulator (STI) rapidly followed the theoretical predictions. In contrast, the weak
topological insulator has so far eluded experimental verification, since the topological surface
states emerge only on particular side surfaces which are typically undetectable in real 3D crystals.
In my talk, I will provide experimental evidence for the weak topological insulator (WTI) state ina bismuth iodide, β-Bi4I4. Significantly, the crystal has naturally cleavable top and side planes
both stacked via van-der-Waals forces, which have long been desirable for the experimental
realization of the WTI state. As a definitive signature of it, we find quasi-1D Dirac topologicalsurface state (TSS) at the side-surface (100) while the top-surface (001) is topologically dark
(Fig.1). Furthermore, a crystal transition from the β- to α-phase drives a topological phasetransition from a nontrivial WTI to the trivial insulator around room temperature. The weak
topological phase, viewed as quantum spin Hall (QSH) insulators stacked three-dimensionallywill lay a foundation for new technology benefiting from highly directional spin-currents withlarge density protected against backscattering [1].

Fig. 1: ARPES results for the side surface (left panels) and the top surface (right panles) obtained by nanoARPES. (a1-a3) Fermi surface mapping, and band dispersions for the side surface. (b1) Crystal structureof β-Bi4I4. (b2) Schematic of measurements with nano-ARPES. (b3) Spin-polarized band structure withquasi one dimntion for the side surface. (c1,c2) Same data as (a1-a3), but for the top surface.

[1] R. Noguchi et al., Nature (2018), in press.

18

O18-5
Dynamics and transport in quantum magnets
L. Balents1,
1
Kavli Institute of Theoretical Physics, University of California, Santa Barbara, CA
I will discuss aspects of dynamics and transport in quantum magnets. To be determined.

19

O18-6
Proton-dynamics Coupled Quantum Spin Liquid State
and Magnetic Switching in Organic Mott System
H. Mori1
1
Institute for Solid State Physics, The University of Tokyo, Japan
Novel quantum phases and quatum transport is the central issue in the field of quantum
condensed matter physics and materials sciences. Quantum phenomena are generally observed
as behaviors of electrons by using charge, spin, lattice, and orbitals degrees of freedom.
Moreover, hydrogen as well as electron possesses quantumness due to the lightest atom andaffords a variety of states by coupling of an electron and a proton: H (hydrogen atom), H2
molecule (covaleted hydrogen molecule), H+ (proton), H‒ (hydride), etc.
Recently, we have explored novel phenomena and functionalies with coupling of electron
and proton [1-5]. As a result, (1) metallic state of purely organic conductor based upon
protonated single units under 1 GPa for κ-H3(Cat-EDT-ST)2, [2] , (2) quatum spin liquid statewith coupling of quantum fluctuaion of proton for κ-H3(Cat-EDT-TTF)2 [2,3,5], and (3)magnetism and conductivity switching as large deuterium isotope effect with ∆Tc = 185 K forκ-D3(Cat-EDT-TTF)2 [4] have been discovered.
This research has been carried out by the collaboration with Mr. T. Takakura, Drs. A. Ueda
J. Yoshida, M. Shimozawa, M. Yamashita, J. Gouchi, Y. Uwatoko (ISSP), A. Nakao (CROSS),K. Kobayashi, R. Kumai, H. Nakao, Y. Murakami (KEK-PF), K. Takahashi (Kobe Univ.), T.
Isono, S. Uji (NIMS), and K. Yamamoto (Okayama Sci. Univ.)

Figure 1: Quantum spin liquid state, and magnetism and conductivity switching inorganic proton-electoron coupled systems, κ-X3(Cat-EDT-TTF)2 [X = H, D].

[1] H. Kamo, A. Ueda, H. Mori, et al., Tetrahedron Lett. 53, 4385 (2012).
[2] T. Isono, A. Ueda, H. Mori et al., Nature Commun. 4 (2013) 1344(1-6).
[3] T. Isono, A. Ueda, H. Mori, Phys. Rev. Lett., 112, 177201 (2014).
[4] A. Ueda, H. Mori, et al., J. Am. Chem. Soc., 136, 12184–12192 (2014); Chem. Eur.J., 21,
15020 (2015).
[5] M. Shimozawa, M. Yamashita, A. Ueda, H. Mori, et al., Nature Commun., 8, 1821(1-6)(2017).

20

O18-7
The quantum dipole liquid in triangular lattice molecular
Mott insulators and its relevance to a spin liquid
N. Drichko
Johns Hopkins Univ.
Mott insulators are commonly pictured with electrons localized on lattice sites with their lowenergy physics involving spins only. Using Raman spectroscopy as the main tool, we havedemonstrated the presence of on-site electric dipoles in some molecule-based Mott insulators
on a triangular lattice [1]. In k-(BEDT-TTF)2Hg(SCN)2Br, when electrons localize on atriangular lattice of molecular dimers at temperatures below 100 K, they form electric dipoles
which do not order at low temperatures and fluctuate, resulting in a so-called quantum dipole
liquid state. A collective mode of dipole fluctuations is observed in Raman spectra at 1.3 THz.
In the sister compound k-(BEDT-TTF)2Hg(SCN)2Cl, on-site electric dipoles order below 30 K,
however we demonstrate that at lower temperatures this charge order melts. According to ourrecent results, this material shows paramagnetic behavior down to low temperatures suggestiveof a spin liquid state.

[1] N. Hassan et al. Science (2018).

21

O18-8
Theory of proton-driven quantum spin-dipole liquid
Masahiko G. Yamada and Yasuhiro Tada,
Institute for Solid State Physics, The University of Tokyo, Japan
Motivated by the recent discovery of coexistence of unfrozen spin and electric-dipole fluctuations in the organic dimer Mott insulator κ -H3 (Cat-EDT-TTF)2 called H-Cat [1], we presenta theory of a new quantum liquid state based on a model of hydrogen-bonded systems where
electrons are coupled with quantum proton motion. There are macroscopically degenerate groundstates in the classical limit, and quantum fluctuations of the proton motion will lift the degeneracy.
The resulting quantum ground state can be regarded as a variant of the U(1) spin liquid in threespatial dimensions. We also discuss implications for the experiments in H-Cat and its deuterated
analog D-Cat.

[1] M. Shimozawa et al., Nat. Commun., 8, 1821 (2017).

22

O18-9Voltage control of magnetic anisotropy and its application
to voltage-torque MRAM
Shinji Yuasa1, Takayuki Nozaki1, Tatsuya Yamamoto1, Masahito Tsujikawa2,3,
Masafumi Shirai2,31National Institute of Advanced Industrial Science and Technology (AIST), Japan
2
Research Institute of Electrical Communication, Tohoku University, Japan
3
Center for Spintronics Research Network (CSRN), Tohoku University, Japan
Voltage control of spin enables both a zero standby power and ultralow active power
consumption in spintronic devices such as magnetoresistive random-access memory MRAM.
A practical approach to achieve voltage control is the electrical modulation of the spin–orbit
interaction at the interface between 3d-transition-ferromagnetic-metal and dielectric layers in amagnetic tunnel junction (MTJ). However, we need to initiate a new guideline for materials
design to improve both the voltage-controlled magnetic anisotropy (VCMA) and perpendicularmagnetic anisotropy (PMA). We report that atomic-scale doping of iridium in an ultrathin Fe
layer is highly effective to improving these properties in Fe/MgO-based MTJs. Iridium doping
yielded both a large enhancement of PMA and a huge VCMA coefficient (up to 320 fJ/Vm)
with high-speed response [1,2]. First-principles calculations revealed that Ir atoms dispersed
within the Fe layer play a considerable role in enhancing PMA and the VCMA coefficient.
These results demonstrate the efficacy of heavy-metal doping in ferromagnetic layers as anadvanced approach to develop high-density voltage-driven spintronic devices. We also reporton experimental evaluation of write error rate (WER) of voltage-induced dynamical switching
and its theoretical analyses based on macro-spin model [3-4]. We show a good agreement
between experimental results and theory. This work was supported by the ImPACT Program of
the Council for Science, Technology and Innovation.
[1] T. Nozaki et al., NPG Asia Materials 9, e451 (2017).
[2] T. Nozaki et al., APL Materials 6, 026101 (2018).
[3] T. Yamamoto et al., Phys. Rev. Applied 10, 024004 (2018).
[4] T. Yamamoto et al., Phys. Rev. Applied 11, 014013 (2019).

23

O18-10
Electric-field-induced change of perpendicular magnetic
anisotropy at metal/dielectric interface
S. Miwa1,2
1
The Institute for Solid State Physics, The University of Tokyo, Japan
2
Center for Spintronics Research Network, Osaka University, Japan
Electric-field-induced control of magnetic properties at room temperature has attracted
considerable attention owing to its significant potential for facilitating the construction ofultralow-power-consumption electric devices. Voltage-controlled magnetic anisotropy(VCMA) in ferromagnetic metallic multilayered structure [1,2] has shown that magnetization
can be controlled in fast periods (down to 0.1 ns) by electric fields, as indicated by bi-stableprecessional magnetization switching, and ferromagnetic resonance excitation. Because the
VCMA mechanism can be purely electronic, this is an ultimate technology for the operation of
spintronics devices, such as nonvolatile random access memory, where high-speed operation
with high writing endurance is indispensable.
In this talk, we will show a microscopic origin of the VCMA effect [3-5]. Firstly, VCMA
effect in 3d-transition metals can be explained by electric-field-induced change of orbital
magnetic moment, that is, charge doping effect. We show it in terms of X-ray magnetic
circular dichroism (XMCD) spectroscopy of Co-absorption edge on Fe-Co-MgO multilayer [3].
Secondly, VCMA effect in 5d-transition metals can be explained by both electric-field-inducedchanges of orbital magnetic moment and magnetic dipole Tz term, that is, charge redistribution
effect. We show it in terms of XMCD spectroscopy of Pt-absorption edge on Fe-Pt-MgO
multilayer. Specifically, the magnetic dipole Tz induction is correlated to an electric
quadrupole induction in interfacial metallic atoms with MgO tunnel barrier, and it changes theperpendicular magnetic anisotropy energy through spin-flip virtual excitation process. Such an
electric quadrupole induction can be feasible due to nonlinear electric field potential because of
the strong electrostatic screening effect in metals [5].
This work is a collaboration work with Y. Suzuki, F. Bonell, K. Matsuda, T. Tsukahara, T.
Kawabe, J. Suwardy, K. Nawaoka, M. Goto, and E. Tamura of Osaka University, M. Suzuki,
Y. Kotani, K. Toyoki, and T. Nakamura of JASRI, T. Nozaki, and S. Yuasa of AIST, M.
Tsujikawa, and M. Shirai of Tohoku University, T. Ohkubo, and K. Hono of NIMS.
[1] M. Weisheit et al., Science 315, 349 (2007)[2] T. Maruyama et al., Nat. Nanotechnol. 4, 158 (2009)[3] T. Kawabe et al., Phys. Rev. B 96, 220412(R) (2017)[4] S. Miwa et al., Nat. Commun. 8, 15848 (2017)[5] S. Miwa et al., J. Phys. D: Appl. Phys. 52, 063001 (2019).

24

O18-11Ultrafast demagnetization in Pt-containing ferromagnetic
thin films probed by x-ray free electron laser
K. Yamamoto1,2, Y. Kubota3, M. Suzuki3, Y. Hirata1, 2, K. Takubo1, Y. Uemura4,
R. Fukaya5, K. Tanaka6, W. Nishimura6, T. Ohkochi3, T. Katayama3, T. Togashi3,
K. Tamasaku7, M. Yabashi3, 7, Y. Tanaka6, T. Seki8,9, K. Takanashi8,9 and H. Wadati1,21
Institute for Solid State Physics, The University of Tokyo, Japan2
Department of Physics, The University of Tokyo, Japan
3
Japan Synchrotron Radiation Research Institute, Japan
4
Institute for Molecular Science, Japan
5
Institute of Materials Structure Science, High Energy Accelerator Research
Organization, Japan
6
Graduate School of Material Science, University of Hyogo, Japan
7
RIKEN SPring-8 Center, Japan
8
Institute for Materials Research, Tohoku University, Japan
9
Center for Spintronics Research Network, Tohoku University, Japan
In recent times, photo-induced magnetism has attracted significant attention fromresearchers because of its non-trivial mechanism and avenues for practical application.
Considering this, to understand the mechanism of photo-induced magnetization dynamics,
element-specific measurements are necessary because magnetic materials that show
remarkable photo-induced behaviors contain more than one magnetic element. X-ray freeelectron laser is useful for this purpose because of its ultrashort pulses and tenability of photon
energy and we can perform time-resolved element-specific magnetic dynamics measurementby core level absorption.
We demonstrate ultrafast magnetization dynamics in a 5d transition metal using circularlypolarized x-ray free electron laser in the hard x-ray region[1]. A decay time of light-induced
demagnetization of L10-FePt was determined to be τPt = 0.6 ps using time-resolved x-ray
magnetic circular dichroism at the Pt L3 edge as shown in Fig. 1, whereas magneto-optical
Kerr measurements indicated the decay time fortotal magnetization as τtotal = 0.1 ps. A transientmagnetic state with the photo-modulated
magnetic coupling between the 3d and 5delements is firstly demonstrated. We also carriedout time-resolved resonant magneto optical Kerr
effect measurement for ferromagnetic multilayer
thin film and obtained consistent results.
Figure 1: Time-resolved x-ray magnetic
circular dichroism of FePt at Pt L edge.
[1] K. Yamamoto et al., arXiv:1810.02551.

25

O19-1
Magic Angle Twisted Bilayer Graphene
Allan H. MacDonald
Physics Department, University of Texas at Austin

Magic Angle Twisted Bilayer Graphene (MATBG) is a remarkably tunable and relatively
simple strongly correlated electron system, with its own set of specific peculiarities. My talkwill focus on similarities and differences between the interaction physics of flat-band moiré
superlattices in transition metal dichalcogenide bilayers, which are well described by singleband Hubbard models, and the corresponding interaction physics in MATBG systems, which
are not. I will discuss the nature of the insulating ground states and the collective excitation
spectra at 1/2, 1/4, and 3/4 filling of the moiré conduction and valence bands, address the issueof finding the optimal compromise between simplicity and accuracy in the construction ofmodels suitable for analysis in the strong coupling limit, and speculate on the relationshipbetween the insulating states and their collective models and the superconducting domes.

26

O19-2Anomalous transverse transport and domain wall motion
in non-collinear antiferromagnets
T. Nomoto1 and R. Arita1,2
1Department of Applied Physics, The University of Tokyo, Japan
2
RIKEN Center for Emergent Matter Science
Recently, Mn3Sn has attracted considerable attention as a magnetic Weyl semimetal [1]exhibiting a large anomalous Hall effect [2,3,4] and anomalous Nernst effect [5,6]. While theseeffects are usually observed in ferromagnets, the net (uniform) magnetization is vanishingsmall in the non-collinear antiferromagnetic structure of Mn3Sn. Interestingly, this magnetic
structure can be viewed as ferroic ordering of cluster magnetic octupoles. In fact, this octupole
can induce anomalous transverse transport, since its irreducible representation is the same asthat of the magnetization (magnetic dipole) [7]. More recently, Higo et al. have observed alarge magneto-optical Kerr effect in Mn3Sn, and succeeded in visualizing magnetic octupole
domains and their reversal [8].
Motivated by this experiment, we perform numerical simulations with the atomistic
Landau-Lifshitz-Gilbert (LLG) equation and investigate the dynamics of a domain wall in
Mn3Sn. We show that the spin-orbit torque drives the domain wall much faster than that inferromagnets. Next, we rewrite the LLG equation in terms of cluster multipoles and derive anequation of motion for the magnetic octupole, which can be solved analytically. The analyticalsolution reproduces the numerical simulation very accurately. This result indicates that thecluster magnetic octupole is a useful order parameter to describe the domain wall motion andspin dynamics in non-collinear antiferromagnets.
[1]
[2]
[3]
[4]
[5]
[6]
[7]
[8]

K. Kuroda et al., Nature Materials, 16 1090-1095 (2017).
J. Kuebler and C. Felser, Europhys. Lett. 108, 67001 (2014).
S. Nakatsuji, N. Kiyohara, and T. Higo, Nature 527, 212 (2015).
A. K. Nayak et al., Sci. Adv. 2, e1501870 (2016).
X. Li et al., Phys. Rev. Lett. 119, 056601 (2017).
M. Ikhlas, et al., Nature Physics 13 1085 (2017).
M.-T. Suzuki, T. Koretsune, M. Ochi and R. Arita, Phys. Rev. B. 95, 094406 (2017).
T. Higo et al., Nature Photonics 12 73 (2018).

27

O19-3

Crystal symmetries and transport phenomena in
antiferromagnets
1

Tomas Jungwirth1,2Institute of Physics, Academy of Sciences of the Czech Republic, Czech Republic
2
School of Physics and Astronomy, University of Nottingham, United Kingdom

The suppression of dipolar fields in antiferromagnets is favorable for high density integrationof memory elements and makes them robust against magnetic field perturbations. Other
unique merits of antiferromagnetic spintronics include the multi-level switching, suitable for
integrating memory with logic or neuromorphic functionalities, and the ultra-fast THz spin
dynamics. In the lecture we will first give a brief overview of the multiple directions incurrent research of antiferromagnetic spintronics [1]. We will then outline the rich symmetry
and topology landscape of antiferromagnets which allows for a range of transport phenomena
suitable for manipulating and detecting antiferromagnetic spins. Our main focus will be onelectrical readout of 180o spin-reversal in collinear antiferromagnets [2]. Apart frommicroscopic imaging of a domain wall motion, this can be facilitated by a second-ordermagnetoresistance effect in antiferromagnets with broken time and space-inversion
symmetries. In the linear response, the magnetic structure alone cannot generate aspontaneous Hall effect collinear antiferromagnets. However, we introduce a mechanism andcorresponding candidate collinear antiferromagnets, in which the breaking of time-reversal
and other symmetries required by the Hall effect is caused by the arrangement of nonmagnetic atoms in the lattice. Hall conductivities as large as 1000 S/cm are obtained in our
first-principles calculations which originate from spin-orbit coupled bands with topologicalsignatures linked to the remaining crystal symmetries in the considered collinear
antiferromagnets.
[1] T. Jungwirth et al., Nature Physics 14, 200 (2018).
[2] J. Godinho et al., Nature Communications 9, 4686 (2018).

28

O19-4Large time-reversal-odd responses
in the Weyl antiferromagnet Mn3Sn bulk and thin film
for antiferromagnetic spintronics
T. Higo1,2, H. Man1, M. Ikhlas1, D. Qu1, D.B. Gopman3, Y.P. Kabanov3, O.M.J. van ’t
Erve4, Liang Wu5,6, D. Rees6, S. Patankar6, Yufan Li7, T. Koretsune8, M.-T. Suzuki8,
R.D. Shull3, J. Orenstein6, C.L. Chien7, R. Arita9,10, Y. Otani1,2,9 and S. Nakatsuji1,2,7
1
Institute for Solid State Physics, The University of Tokyo, Japan
2
CREST, Japan Science and Technology Agency (JST), Japan
In the last few years, there has been a surge of interest in antiferromagnetic (AF) materials
due to their favorable properties including vanishingly small stray ﬁeld, faster spin dynamics,
and abundance in nature compared to their FM counterparts [1]. In fact, motivated by these
intriguing properties, several breakthroughs have been made; for example, the anisotropic
magnetoresistance (AMR), even-function response under time-reversal (TR), has been founduseful for detecting the collinear AF ordering [2]. Another breakthrough is the discovery of
odd-function response under TR in Mn3Sn such as anomalous Hall [3] and Nernst [4] effects,
magneto-optical Kerr effect (MOKE) [5] and a novel type of (magnetic) spin Hall effect [6] atzero magnetic field. Moreover, experimental studies have shown that Mn3Sn is the ﬁrst version
of a Weyl magnet where the Weyl fermions near the Fermi energy give rise to the TR-odd
topological responses [7]. In this talk, we will propose the Weyl antiferromagnet Mn3Sn as apromising material for the AF spintronics. This is because Mn3Sn exhibits the large TR-odd
responses such as the anomalous Hall effect at zero magnetic field [3], and these spontaneous
responses can be controled by the AF domain with ferroic ordering of the magnetic octopole
which has been observed by the MOKE [5]. We will also show that not only the bulk crystals
but also Mn3Sn thin films exhibit large TR-odd responses [8], which provides an important
step for further developing spintronics devices using AF materials.
3

NIST, USA. 4US Naval Research Laboratory, USA. 5University of California, Berkeley,USA. 6University of Pennsylvania, USA. 7Johns Hopkins University, USA. 8Tohoku University,
Japan. 9RIKEN-CEMS, Japan. 10University of Tokyo, Japan.
[1] T. Jungwirth et al., Nat. Nanotech. 5, 231 (2016).
[2] X. Marti et al., Nat. Mater. 13, 367 (2014); P. Wadley et al. Science 351, 587 (2016).
[3] S. Nakatsuji, N. Kiyohara, and T. Higo, Nature 527, 212 (2015).
[4] M. Ikhlas, T. Tomita et al., Nat. Phys. 13, 1085 (2017).
[5] T. Higo et al., Nat. Photon. 12, 73 (2018).
[6] M. Kimata et al., Nature (in press).
[7] K. Kuroda, T. Tomita et al., Nat. Mater. 16, 1090 (2017).
[8] T. Higo et al., Appl. Phys. Lett. 113, 202402 (2018).

29

O19-5Observation of magnetic spin Hall effect and magnetic
inverse spin Hall effect in a chiral antiferromagnet Mn3Sn
K. Kondou1,2, M. Kimata2,3, H. Chen4,5, S. Sugimoto3, P. K. Muduli3, M. Ikhlas3,
Y. Omori3, T. Tomita2,3, A. H. MacDonald4, S. Nakatsuji2,3 and Y. Otani1,2,3
1
Center for Emergent Matter Science, RIKEN, Japan.
2
CREST, Japan Science and Technology Agency (JST), Japan.
3
Institute for Solid State Physics, University of Tokyo, Japan.
4
Department of Physics, University of Texas at Austin, USA.
5
Department of Physics, Colorado State University, USA.
Spin Hall effect provides the spin-charge interconversion in non-magnetic materials, which
has drawn much attention because of its potential application for efficient magnetization
switching via the spin-transfer torque [1].
Here we focus on the non-collinear antiferromagnet Mn3Sn to realize the new functionality
in spin-charge conversion. M3Sn exhibits the large anomalous Hall effect comparable withferromagnet at room temperature [2]. Figure 1 shows a devise structure for spin accumulation
detection. By applying the charge current on a Mn3Sn strip, spin accumulation can be detected
electrically by the ferromagnetic electrode. This technique enables us to observe the SHE in
Mn3Sn, exhibiting an anomalous sign change when its small magnetic moment switchesorientation. Additionally, we succeeded in observation of the sign change in the inverse effectby means of spin pumping method. By comparison with theoretical toy-model, we found thatsuch unique functionality in Mn3Sn is caused by the momentum-dependent spin splitting
produced by non-collinear magnetic order [3].

Figure 1 Device structure for spin accumulation detection a, SEM image of spin
accumulation device b, Measurement setup. The electrical current was applied along [-12-10]
direction. The external magnetic field was rotated within the device basal plane and the field
angle θ was measured from the [01-10] axis. c, Spin accumulation signals. Magnetic fielddependence of the resistance measured between NiFe-Cu electrodes at room temperature.

[1] L. Liu et al., Science 336, 555 (2012). [2] S. Nakatsuji, N. Kiyohara and T. Higo, Nature
527, 212 (2015). [3] M. Kimata, et al., Nature (in press) DOI: 10.1038/s41586-018-0853-0.

30

O19-6
Majorana fermions and half-integer thermal quantum Hall
effect in a quantum spin liquid
Y. Matsuda1, Y. Kasahara1, T. Ohnishi1, K. Sugii2, Sixiao Ma1, Y. Mizukami3,
O. Tanaka3, N. Kurita4, H. Tanaka4, M. Shimozawa2, M. Yamashita2, J. Nasu4,
Y. Motome5, and T. Shibauchi3,
12Department of Physics, Kyoto University, Kyoto, Japan

Institute for Solid State Physics, The University of Tokyo, Japan3

Department of Advanced Materials Science, The University ofTokyo, Japan
4
Department of Physics, Tokyo Institute of Technology, Tokyo, Japan
5
Department of Applied Physics, The University of Tokyo, Tokyo,
Japan

The quantum Hall effect (QHE) is one of the most remarkable phenomena incontemporary condensed matter physics, which rivals superconductivity in its
fundamental significance as a manifestation of quantum mechanics on a macroscopic
scale. The quantum Hall state is a topological property of quantum matter. There are
two classes of the QHE, where integer and fractional electrical conductance aremeasured in units of e2/h. Here we report a novel type of quantization of the Hall
effect caused by charge neutral quasiparticles, i.e. Majorana fermions, in an insulating
two-dimensional (2D) quantum magnet, -RuCl3 with honeycomb lattice[1][2]. This
material has been suggested to be a candidate of Kitaev quantum spin liquid (QSL),
where significant entanglement of quantum spins is expected. In the low-temperature
regime of the QSL state, the 2D thermal Hall conductance reaches a quantum plateau
as a function of applied magnetic field. Surprisingly, the plateau attains a quantization
value xy/T=1/2(2kB2/3h), which is exactly half of that in the integer QHE. This halfinteger thermal Hall conductance observed in a bulk material is a direct signature of
topologically protected chiral edge currents of emergent Majorana fermions, whose
degrees of freedom are half of those of electrons, and non-Abelian anyons in the bulk.
[1]Y. Kasahara et al. Phys. Rev. Lett. 120, 217205 (2018).
[2]Y. Kasahara et al. Nature 559, 227 (2018).

31

O19-7Spin Thermal Hall Conductivity of a Kagomé
Antiferromagnet
Minoru Yamashita
Institute for Solid State Physics, The University of Tokyo, Japan
Searching for the ground state of a kagomé Heisenberg antiferromagnet(KHA) has been one of the central issues of condensed-matter physics, because the
KHA is expected to host spin-liquid phases with exotic elementary excitations.
To study the elementary excitations, we investigate the longitudinal (𝜅𝜅𝑥𝑥𝑥𝑥 ) andtransverse ( 𝜅𝜅𝑥𝑥𝑥𝑥 ) thermal conductivities of a new candidate of 𝑆𝑆 = 1/2 KHA Ca

kapellasite (CaCu3(OH)6Cl2⋅0.6H2O) [1]. We find a clear thermal Hall signal in thespin liquid phase of 𝑇𝑇 ∗ < 𝑇𝑇 < 𝐽𝐽/𝑘𝑘𝐵𝐵 , where 𝑇𝑇 ∗ ∼ 7 K is the magnetic transition
temperature and 𝐽𝐽⁄𝑘𝑘𝐵𝐵 ∼ 66 K is the effective spin interaction energy [2]. The
temperature dependence of 𝜅𝜅𝑥𝑥𝑥𝑥 /𝑇𝑇 shows an increase as lowering temperature below
𝐽𝐽/𝑘𝑘𝐵𝐵 , which is followed by a peak at 𝑇𝑇 ∼ 𝐽𝐽⁄3𝑘𝑘𝐵𝐵 . We find that 𝜅𝜅𝑥𝑥𝑥𝑥 is well reproduced,
both qualitatively and quantitatively, by the Schwinger-boson mean-field theory [3]with the Dzyaloshinskii-Moriya interaction of 𝐷𝐷⁄𝐽𝐽 = 0.1 − 0.3 . Most remarkably,both 𝜅𝜅𝑥𝑥𝑥𝑥 of Ca kapellasite and that of another kagomé antiferromagnet volborthite[4] are found to converge to one single curve of our Schwinger-boson calculation only
by choosing 𝐽𝐽 and 𝐷𝐷 as fitting parameters. This excellent agreement demonstrates
not only that the thermal Hall effect in these kagomé antiferromagnets is caused by
spins in the spin liquid phase, but also that 𝜅𝜅𝑥𝑥𝑥𝑥 is given by a simple scaling function
𝑓𝑓(𝑘𝑘𝐵𝐵 𝑇𝑇⁄𝐽𝐽), unveiling the spin 𝜅𝜅𝑥𝑥𝑥𝑥 (𝑇𝑇) of KHA.
We further find that 𝜅𝜅𝑥𝑥𝑥𝑥 of another kagomé compound, Cd kapellasite [5], canalso be well reproduced by the same scaling function with smaller 𝐽𝐽 . This isconsistent with that 𝐽𝐽 of Cd kapellasite is estimated as smaller than that of Ca
kapellasite, demonstrating the validity of our scaling.
This work has been done in collaboration with M. Akazawa, H. Doki, Jung
Hoon Han, Z. Hiroi, N. Kawashima, Hyun-Yong Lee, M. Oda, R. Okuma, M.
Shimozawa, K. Sugii, and H. Yoshida.
References[1] H. Yoshida et al., J. Phys. Soc. Jpn. 86, 033704 (2017).
[2] H. Doki, M. Akazawa, Hyun-Yong Lee, et al., Phys. Rev. Lett. 121, 097203 (2018).
[3] H. Lee, J. H. Han, and P. A. Lee, Phys. Rev. B 91, 125413 (2015).
[4] D. Watanabe, et al., Proc. Natl. Acad. Sci. 113, 8653-8657 (2016).
[5] R. Okuma et al., Phys. Rev. B 95, 094427 (2017).
[6] M. Akazawa, et al., in preparation.

32

O19-8Gapless spin liquid in the anisotropic triangular lattice
antiferromagnet A3ReO5Cl2 (A = Ca, Sr, Ba)
D. Hirai1, T. Yajima1, K. Nawa2, M. Kawamura1, T. Misawa1 and Z. Hiroi1
1
Institute for Solid State Physics, The University of Tokyo, Japan
2
IMRAM, Tohoku University, JapanThe anisotropic triangular lattice (ATL) provides us with a unique playground for studying
spin liquids existing between one and two dimensions. Anisotropy of the magnetic interaction
on the triangular lattice is expected to lead to a variety of quantum phases including spiralorder, gapless and gapped spin liquid phases [1, 2]. However, the number of model compounds
is limited.
We report here new 5d quantum antiferromagnets A3ReO5Cl2 (A = Ca, Sr, and Ba) [3],where Re6+ ions carrying Heisenberg spin-1/2 form an ATL (Fig. 1a). Each of thesecompounds shows a broad peak in the temperature dependences of magnetic susceptibility (Fig.
1b), which is nicely fitted by the Heisenberg spin-1/2 ATL model. In spite of the substantial
two-dimensionality, one-dimensionality is clearly observed in the heat capacity data: a T-linear
heat capacity with a consistent magnitude of the coefficient indicative of a gapless spin
excitation is observed at low temperatures. This reduction of dimensionality from ATL to
decoupled spin chains must be caused by geometrical frustration. This family of compounds
can be a good model system to study the Heisenberg spin-1/2 ATL in a systematic way.

Figure 1: (a) Anisotropic triangular lattice fromed by Re6+ (S = 1/2) ions in A3ReO5Cl2 (A = Ca,Sr, and Ba). (b) Temperature dependence of magnetic susceptibility of A3ReO5Cl2.

[1] R.R.P. Singh and D.A. Huse, Phys. Rev. Lett. 68, 1766 (1992).
[2] S. Yunoki and S. Sorella, Phys. Rev. B 74, 014408 (2006).
[3] D. Hirai et al., J. Am. Chem. Soc. 139, 10784 (2017).

33

O20-1
Nonreciprocal transport in quantum materials
N. Nagaosa
RIKEN Center for Emergent Matter Science (CEMS), Japan
Department of Applied Physics, The University of Tokyo, Japan
When the system lacks both parity and mirror symmetries, it is called “chiral” and can beclassified into right-handed and left-handed. Chirality is one of the most fundamental issue inmany branches of sciences [1]. In physics, especially the dynamics of chiral matters is an
important issue. In this talk, I will discuss that the most fundamental principles in physics
manifest themselves in the nonreciprocal transport phenomea in chiral systems, i.e., thesymmetries, dissipation, quantum-classical crossover/transition, quantal Berry phase andtopology, and many-body correlation effects [2]. The concrete examples to discuss include
magnetochiral anisotropy of semiconductors [3], Weyl semimetals [4], and superconductors[5], nonlinear spin current generation in Rashba-Dresselhaus systems, and shift currents underphoto-excitations [6].
The collaborators of these works are T. Morimoto, K.W. Kim, R. Wakatsuki, K. Hamamoto,
M. Ezawa, H. Ishizuka, S. Hoshino, S.Koshikawa, S.Shimizu, Y.Kaneko Y. Saito, T. Ideue, Y.
Iwasa, and Y. Tokura.
References[1] M. Gardner, The Ambidextrous Universe. Left, Right and the Fall of Parity,
Basic Books Inc. (1964)[2] Y. Tokur aand N.Nagaosa, Nature Communications 9, 3740 (2018).
[3] T. Ideue et al., Nature Physics 13, 578-583 (2017).
[4] T. Morimoto and N. Nagaosa, Phys. Rev. Lett. 117, 146603 (2016).
[5] R. Wakatsuki et al., Science Advances 3, e1602390 (2017)[6] T. Morimoto and N. Nagaosa,
Science Advances 2, e1501524 (2016).

34

O20-2
Skyrmion lattice in f-electron magnet EuPtSi
K. Kaneko1,2
1 Materials Sciences Research Center, Japan Atomic Energy Agency, Japan
2 J-PARC Center, Japan Atomic Energy Agency, JapanThe lack of spatial inversion symmetry in a structure results in appearance of antisymmetric interactions, that may induce unconventional states of matter. In cubic B20-type compounds crystallizing in the space group P21 3, as represented by MnSi, a combination of the
Dzyaloshinsky−Moriya and ferromagnetic interactions results in a helimagnetic structure withlong pitch. An application of a magnetic field in MnSi induces a field-induced ordered statewith magnetic skyrmions, particle-like topologically non-trivial spin textures, as evidenced bysmall-angle neutron scattering[1]. Following this discovery, intensive search on skyrmions has
conducted for materials particularly in this space group, that leads to find new class of materials,
such as FeGe[2], Cu2 OSeO3 [3]. Whereas diverse properties of skyrmions have been revealed sofar, materials hosting the skyrmion lattice were mostly limited to 3d -electron systems.
Rare-earth intermetallic compound EuPtSi also crystallizes in the cubic space group P21 3.
Recent study revealed that an application of magnetic fields induces a transition from an antiferromagnetic ground state to a field-induced ordered phase, called A phase, in the intermediate
temperature range[4], that reminds us the skyrmion phase in MnSi. In addition, emergence ofadditional Hall resistivity was confirmed when the system enters into the A phase. A complementary use of neutron diﬀraction, small-angle neutron scattering, and resonant X-ray scattering gives
further microscopic evidence for the formation of the skyrmion lattice in EuPtSi[5, 6]. In contrast
to similarities in the phase diagram and transport, there exists clear diﬀerences with 3d systems,
such as periodicity and anisotropy. This discovery in 4 f electron compound will extend to otherf -electron systems, and help to deepen our understanding on skyrimion physics.

[1] S. Mühlbauer et al., Science 323, 915 (2009).
[2] M. Uchida et al., Phys. Rev. B 77, 184402 (2008).
[3] S. Seki et al., Science 336, 198 (2012).
[4] M. Kakihana et al., J. Phys. Soc. Jpn. 87, 023701 (2018).
[5] K. Kaneko et al., J. Phys. Soc. Jpn. 88, 013702 (2019).
[6] C. Tabata et al., in preparation.

35

O20-3Magnetization of the skyrmion lattice phase andfield-induced tricritical point in EuPtSi
T. Sakakibara1 , S. Kittaka1 , S. Nakamura2 , M. Kakihana3 , Y. Ashitomi3 , M. Hedo4 ,T. Nakama4 , and Y. Ōnuki4
1 Institute for Solid State Physics, The University of Tokyo, Japan
2 Department of Physical Science and Engineering,

Nagoya Institute of Technology, Japan
3 Graduate School of Engineering and Science, University of the Ryukyus, Japan
4 Faculty of Science, University of the Ryukyus, Japan

EuPtSi crystallizes in a cubic chiral structure with the space group P21 3, the same as MnSi.
This compound helimagnetically orders at TN =4.1 K [1, 2]. We examined the magnetic phasetransitions of EuPtSi by means of high-precision magnetization measurements on a high-quality
single crystal, and established the phase diagrams.
The helimagnetic order at TN is known to be weakly first order [1, 2]. This is a fluctuationinduced first-order transition (FOT) [2], which is driven by the interactions between criticalfluctuations of the order parameters when the degrees of freedom of the OP is large. By increasing
the magnetic field, we observed that FOT turns into a second-order transition above a field-induced
tricritical point (TCP). The location of TCP strongly depends on the field direction.
This compound exhibits an exotic magnetic phase (A-phase) in the intermediate field range
within the conical state below TN [3, 4]. Very interestingly, additional Hall resistivity has recently
been observed in this field-induced phase [3], bearing a close resemblance to the skyrmion latticephase in MnSi. The possibility of the skyrmion lattice phase in EuPtSi has further been supportedby the recent neutron diﬀraction measurements [4]. Our magnetization data for H ∥ [100] and[111] clearly indicate that the A-phase is entered from the conical phase accompanied by a sharp
peak in dM/dH ; the phase transition is of first order. The A-phase is stabilized only at finite
temperatures above 0.3 K, depending crucially on the field direction; no A-phase appears for H
near [110] direction. In the ground state below 0.3 K, the A-phase is absent in thermal equilibrium
and the magnetization of the conical state linearly increases with H and saturates near 3 T for all
directions. The magnetic anisotropy of the system is therefore weak as expected for the L = 0
ground state of Eu2+ ions, although the phase diagram is highly anisotropic.

[1] M. Kakihana et al., J. Electron. Mater. 46, 3572 (2017).
[2] D.G. Franco et al., Phys. Rev. B 96, 014401 (2017).
[3] M. Kakihana et al., J. Phys. Soc. Jpn. 87, 023701 (2018).
[4] K. Kaneko et al., J. Phys. Soc. Jpn. 88, 013701 (2019).

36

O20-4
Theory of Multipolar Order and Multipolar Kondo EffectYong Baek Kim1
1
University of Toronto
Motivated by a series of recent experiments on the cubic heavy fermion systems such as
PrTi2Al20 and PrV2Al20, we develop a general Landau theory of multipolar order. Here the nonKramers local moments at Pr sites carry the quadrupolar and octupolar moments, and interact
with conduction electrons. We show how such a theory can be used to predict the genericphase diagram and discuss experimental signatures of the multipolar order. In particular, we
explain how the magnetostriction can be used to detect the multipolar order parameters. The"Kondo"-like effect due to the coupling between the multipolar moments and conduction
electrons will also be discussed.

37

O20-5
Field-induced switching of ferro-quadrupole orderparameters in PrTi2Al20
T. Taniguchi1, K. Hottori2, M. Yoshida1, H. Takeda1, S. Nakamura1, T. Sakakibara1,
M.Tsujuimoto1, A. Sakai1, Y. Matsumoto1, S. Nakatsuji1, and M. Takigawa1
1
Institute for Solid State Physics, The University of Tokyo, Japan2
Department of Physics, Tokyo Metropolitan University, Japan

We report a magnetic-field-induced first order phase transition in the ferro-quadrupole orderedstate of PrTi2Al20, in which non-Kramers Pr3+ ions with two 4f electrons have the non-magnetic
3 doublet ground state in the cubic (Td) crystalline electric field. For the magnetic field along[111], the 27Al-NMR and magnetization experiments revealed that Qz ~ 3z2 - r2 type ferroquadrupole order develops below 2 K independent of magnitude of the field. When the field isapplied along [001] or [110], however, a discontinuous transition is induced by a small field of
1 - 2 T caused by switching of the order parameter within the two dimensional space spanned by
Qz and Qx ~ x2 - y2. A symmetry based analysis as well as mean field calculation of aphenomenological model show that the transition is due to competition between the magnetic
Zeeman and the quadrupole interactions and the latter has highly non-linear field dependence.
This peculiar and anisotropic variation of the quadrupole interaction with magnetic field is very
surprising, which should be related to distinct features of the quadrupole Kondo coupling in thissystem.

38

O20-6
Incommensurate magnetism in heavy fermion systems
Collin Broholm11Department of Physics and Astronomy and Institute for Quantum Matter
Johns Hopkins University, Baltimore, MD USA

Neutrons and muons were used to explore the magnetism of CeNiAsO and CeAuSb2. In bothcases the initial thermal instability of their heavy fermion state is to a long-wavelength
amplitude-modulated incommensurate spin density wave (SDW).
Analyzing crystal field excitations, we show CeNiAsO is an easy plane system. There isa low-T transition to a commensurate non-collinear state that may result from bi-quadraticinteractions. The commensurate phase is however, suppressed by P doping in CeNiAs1-xPxOprior to the transition to a Fermi liquid at xc=0.4.
Tetragonal CeAuSb2 is Ising-like and the orthorhombic amplitude modulated
incommensurate SDW is stable to the lowest T. A magnetic field applied along c yields anincommensurate 2-Q state.
Transport anomalies indicate significant modifications in electronic structure for bothmaterials versus doping and field that we discuss considering this new information about spincorrelations.
[1] Shan Wu and Guy Marcus are major contributors to this work that was supported by the
U.S. Department of Energy, Office of Basic Energy Sciences, Division of Material Sciencesand Engineering under Grant No. DE-FG02-08ER46544 and DE-SC-0019331.

39O20-7
Evaluation of chiral superconductivity in Sr2RuO4
Clifford Hicks
Max-Planck-Institute for Chemical Physics of Solids

Through measurements under uniaxial pressure we have learned many new things about thesuperconductivity of Sr2RuO4. However its superconducting order parameter remains
unresolved. The evidence that it is chiral remains compelling but not definitive. In this seminar,
I will discuss results of heat capacity, muon spin rotation, and scanning SQUID microscopy
measurements on Sr2RuO4 placed under uniaxial pressure, and their implication on thequestion of whether or not the order parameter is chiral.

40

O20-8Spin current in quantum spin liquids and superconductions
Eiji Saitoh1-5
1ERATO-SQR, JST, Japan2
Department of Applied Physics, The University of Tokyo, Japan
3
WPI- AIMR, Tohoku University, Japan
4
IMR, Tohoku University, Japan
5
ASRC, JAEA, Japan
Various types of spin current has been found in condensed matter. Such currents give rise to various
functions of matter, and they have led the recent progress of spintronics physics.
The firstly discovered spin current is so called conduction-electron spin current, detected in terms of
the inverse spin Hall effect [1]. Secondly, we found spin-wave spin current in ferrimagnetic materials,
in which spin waves carry angular momentum when their population is antisymmetric in the
momentum space. Spin-wave spin current can also be created by heat current, which we named thespin Seebek effect. The concept of spin-wave spin current was expanded to other magnetically orderedphases such as antiferromagnets. Thirdly, we recently found that spin current can also be carried byspinons [2]; excitation from quantum spin liquid states.
In my talk, I will give an introduction to spin-wave spin current phenomena in antiferromagnets [3,4]with a well-defined Neel vector, spinon-spin injection into 1D quantum spin liquids, spin induced
phenomena in antiferromagnets with DM interaction, and some related spin-current effects in
antiferromagnets. This work was done with Dr. D. Hou, Dr. Z. Qiu, Dr. D. Hirobe, Dr. T. Kikkawa, Dr.
K. Shiomi, Dr. K. Yamamoto, Prof. Y. Tserkovnyak, Prof. O. Gomonay, and Prof. G.E.W. Bauer.
[1] E. Saitoh et al. "Conversion of spin current into charge current at room temperature: inverse soinHall effect"

Appl.Phys. Let. 88 (2006) 182509.

[2] D. Hirobe, E. Saitoh et al. “One-dimensional spinon spin currents” Nature Phys. 13(2017)20.
[3] Z. Qiu, E. Saitoh et al.“Spin-current probe for phase transition in an Insulators”

Nature Com. 7(2016) 12670.
[4] Z Qiu, E Saitoh et al. “Spin colossal magnetoresistance in an antiferromagnetic insulator” Nature
Mat. (2018).

41

O20-9Mapping the XY ferromagnet in d=2+1
onto electrodynamics

Sayak Dasgupta, Shu Zhang, and Oleg Tchernyshyov
Institute for Quantum Matter and Department of Physics and Astronomy
Johns Hopkins University, USA
Theory of the Kosterlitz-Thouless transition relies on a mapping of the XY ferromagnet in
d=2 onto the classical theory of electrostatics, in which a vortex behaves like a particle with anelectric charge equal to its winding number n. Thus vortices interact via a Coulomb potential
with a logarithmic dependence on the distance. We extend the analogy to the dynamical
phenomena in a d=2+1 spacetime. At low energies, the theory resembles the familiar
electrodynamics with a background magnetic field. A careful examination of high-energy
physics reveals that this particle also carries a magnetic flux proportional to the out-of-plane
spin Sz of the vortex core (Figure 1). Braiding two identical vortices thus yields an extra phaseof 2πnSz. Vortices with integer nSz are bosons and those with half-integer nSz are fermions.

Figure 1: A vortex and its core.

42

O20-10
Shining (THz) light on quantum magnetic systems
N.P. Armitage1,∗
1 Institute for Solid State Physics, The University of Tokyo, Japan∗ Currently Japan Society for the Promotion of Science, International Research Fellow,

University of Tokyo - ISSP
Interacting spin spin systems are considered paradigmatic examples of materials exhibiting
quantum cooperative behavior. Of interest are various classical ground states where various formsof exchange and lattice symmetry conspire to give novel spin textures. Also of interest are various
non-classical ground states in the form of spin-liquids that can be understood as systems with noorder parameter, but macroscopic quantum mechanically entangled degrees of freedom. In thistalk I will review recent work on this topic from my group using time-domain THz spectroscopy toprobe the excitations of these systems. Such experiments allow us to do very detailed spectroscopy
and reveal fine features of the magnetic spectra that might have been overlooked otherwise. I will
cover material systems as diverse as HoMnO3 (a classically ordered multiferroic that has an
unconventional quartic Nd-Mn exchange as evidence by an unusual field dependence to the AF
resonance), FeSe2 S4 (a spin-orbital liquid with spin-orbital triplet excitations), CoNb2 O6 (perhaps
our best example of a 1D Ising chain) at the transverse field critical point, and Yb2 Ti2 O7 (aquantum spin ice). In all cases THz spectroscopy reveals unique features that are hard to probewith other magnetic spectroscopies. I will also discuss our recent work using high field THz tonot just measure, but to control spin systems.

43

P01
Thermal transport properties of
S = 1/2 kagome frustrated Cd-kapallasite
M. Akazawa1, H. Doki1, K. Sugii1, M, Shimozawa1, M. Yamashita1,
H. Y. Lee1, N. Kawashima1, S. Kittaka1, T. Sakakibara1, R. Okuma1, Z. Hiroi1,
and J. H. Han2
1
Institute for Solid State Physics, The University of Tokyo, Japan
2
Sungkyunkwan University, Korea
In recent years, the thermal Hall effect has gained a great interest as an important signature of
the topology. This effect has been observed in paramagnetic phase of kagome antiferromagnets,
volborthite[1] and Ca-kapellasite[2]. These thermal Hall conductivities (𝜅𝑥𝑦 ) are shown to be well
reproduced by Schwinger-boson mean field theory by tuning the Dzyaloshinskii-Moriya
interaction (𝐷) and the exchange interaction energy (𝐽) as fitting parameters.
In my presentation, we report further evidence supporting the agreement between theexperiment and theory from thermal Hall measurements in Cd-Kapellasite CdCu3(OH)6(NO3)2・
H2O[3] which has a smaller 𝐽/𝑘B (~ 45 K) than that of Ca-Kapellasite.
We find that 𝜅𝑥𝑦 of Cd-Kapellasite shows a similar temperature dependence with that of CaKapellasite, but the peak temperature is shifted to a lower temperature with a larger peak value.
This difference is consistent with the smaller 𝐽/𝑘B of Cd-Kapellasite. The good scaling of thesekagome materials strongly indicates that a kagome antiferromagnet has a common spin thermal
Hall effect described by the Schwinger bosons[4].
In addition, we investigated the magnetic field dependence of the longitudinal thermal
conductivity ( 𝜅𝑥𝑥 ). Below 30 K, 𝜅𝑥𝑥 normalized by the zero-field value (𝜅𝑛𝑟𝑚 = 𝜅𝑥𝑥 (𝐻)/𝜅𝑥𝑥 (0)) is dramatically decreasing with increasing magnetic field. The decrease becomes larger
as lowering temperature. As a remarkable feature, 𝜅𝑛𝑟𝑚 shows a hump around 𝐻 = 7 T under 0.3
K whereas the field dependence of the heat capacity shows no anomaly at the field. This indicatesa decrease of scattering of heat carriers at ~ 7 T.
[1] D. Watanabe et al., PNAS 113, 8653 (2016).
[2] H. Doki, M. Akazawa, H. Y. Lee et al., Phys. Rev. Lett. 121, 097203 (2018).
[3] R. Okuma et al., Phys. Rev. B 95, 094427 (2017).
[4] M. Akazawa, in preparation.

44

P02
Spin-density-wave transition and Seebeck coefficient inquasi-one-dimensional organic conductors
Y. Asaka, M. Tsujimura, Y. Fuseya
Department of Engineering Science, University of Electro-Communications, Japan

In 2016, a huge magnitude of the Seebeck coefficient was found below the spin-densitywave (SDW) transition temperature (TSDW) in the quasi-one-dimensional organic conductor(TMTSF)2PF6 [1]. The property of the Seebeck coefficient can be divided into two regionswith respect to temperature. In the high temperature region (1K<T<TSDW~12K), the magnitudeof Seebeck coefficient first increases shows a peak around 1~2K, and then decreases bylowering temperature, i.e., it shows a dome structure as a function of temperature. In the lowtemperature region (T<1K), the Seebeck coefficient keeps increasing with lowering
temperature. The purpose of our theoretical research is to clarify the behavior of Seebeckcoefficient in the high temperature region.
The theoretical approaches based on the Boltzmann equation have succeeded in explaining
various thermoelectric properties in metals [**]. However, the Boltzmann equation isapplicable to good metals, so that it is inappropriate to use it below TSDW since it is no more agood metal. On the other hand, there is no restriction for the approaches based on the Kubo
formula. It is applicable both to metals and insulators.
In the present work, we calculate the thermoelectric coefficient by using the Kubo formulaon the basis of the gravitational potential method first introduced by Luttinger [2] andimproved by Jonson and Mahan [3]. We employ the effective tight-binding model of(TMTSF)2PF6 and take into account the opening of the SDW gap and the residual Fermi
surface due to imperfect nesting condition [4][5]. In our calculation, the self-energy was taken
to be constant and deviation of chemical potential due to impurities was considered. As a result,the dome structure observed in the high temperature region was explained quantitatively.

[1] Y. Machida, X. Lin, W. Kang, K. Izawa and K. Behnia, Phys. Rev. Lett 116, 087003(2016).
[2] J. M. Luttinger, Phys. Rev 135, A1505 (1964).
[3] M. Jonson and G. D. Mahan, Phys. Rev. B 21, 4223 (1980).
[4] Y. Fuseya, C. Bourbonnais and K. Miyake, Europhys. Lett 100, 57008 (2012).
[5] M. Shahbazi, Y. Fuseya, H. Bakrim, A. Sedeki and C. Bourbonnais, Phys. Rev. B 95,
165111 (2017).

45

P03
Theoretical study on magnetoresistance of SrTiO3
Y. Awashima, M. Owada, Y,Fuseya
Department of Engineering Science, University of Electro-Communications,
Chofu, Tokyo 182-8585, Japan
It is well known that semimetals and multivalley systems show a magnetoresistance(MR) [1,2]. It is also well known that the system of single type of carrier with the closed fermi
surface does not show the MR according to the conventional Boltzmann theory, even if theanisotropy of the fermi surface is taken into account [1]. Experimentally, however, all systemof single type carrier with closed fermi surface show the MR. For example, SrTiO3 (STO),
which has a closed constant-energy surface at the Γ point, exhibits a clear MR experimentally[3]. The nature of this magnetoresistance has not been clarified yet.
Here, in order to solve this problem, we investigate the effect of the detailed structure of
the Fermi surface, which is slightly deformed from a perfect sphere. We reformulate theconventional Boltzmann theory in order to take into account the arbitrary shape of the Fermi
surface. The new formula so obtained is valid for a strong magnetic field region. First, westudy the effect of the deviation from a sphere on the MR by using cubic harmonics to express
the deviation. We found that a system with the single closed Fermi surfaces shows a clear MR
due to the deviation from a sphere. Next, we employed the effective model of STO [4] andcalculate its MR by the newly obtained formula. We obtained a clear MR for STO, which
agrees with experimental results qualitatively.

Figure 1: fermi surafece of STO(n type,heavy electron)

Figure 2: Magnetoresistance of STO(Transverese)[1] G. Grosso, and G.Parravicini, Solid State Physics (Academic press,2014 )[2] Z. Zhu, B. Fauque, K. Behnia, Y. Fuseya, J.Phys.: Condensed. Matter., 30, 31 (2018).
[3] K. Behnia, B. Fauque, et al., private communication.
[4] H. Uwe, R. Yoshizaki, and T. Sakudo, J. J. Appl. Phys., 24, 335 (1985)

46

P04

Strongly anisotropic high temperature Fermi surface of the
Kondo semimetal CeNiSn revealed by ARPES
C. Bareille1 , T.-S. Nam2 , T. Takabatake3 , T. Yajima1 , M. Nakayama1 , K. Kuroda1 ,B.-I. Min2 , S. Shin1 and T. Kondo1
1 Institute for Solid State Physics, The University of Tokyo, Japan
2 Department of Physics, POSTECH, Korea
3 Graduate School of Advanced Sciences of Matter, Hiroshima University, Japan

nodal line

In heavy fermion system, the screening by the conduction electrons of magnetic moments
yield by the f -electrons commonly gives rise to a metallic heavy Fermi liquid at low temperature.
Namely, this is the Kondo effect in a periodic array of local moments. In terms of band structure, it
can be described as the hybridization between a localized f -level and a conduction band, opening
an indirect gap. Depending on the f -level filling, the chemical potential may lie within the gap:
the expected low temperature metallic state gives way to an insulating phase. The family of Kondo
insulators grew up in the last decades. However, with improvements made on samples quality,
some members turn out to show semimetallic behavior at low temperature.
It is the case of CeNiSn which, with a coherence temperα1α2bΓature as low as 8 K, was believed to be a narrow gap Kondo aZ
insulator, until its resistivity was found to form plateau at low
β1β2
temperature [1]. This semimetallic behavior has been ascribed
nodal
Χ
U
line
to a node in the Kondo hybridization derived from a particularsymmetry of the f -orbitals ground-state [2]. Here we carryU Z
X
out a 3D ARPES study in the high temperature regime to check
whether or not the geometry of the CeNiSn conduction bandR
is compatible with the nodal metal scenario.
S
R
Highly anisotropic Fermi sheets are observed in the form
Figure 1: a. Fermi surface fromof quasi-one and a quasi-two dimensional Fermi sheets, with aOpen core GGA+SOC calculations.
fairly good agreement with our Open core GGA+SOC calcula- b. 2D Fermi sheet at high tempertions, Fig.1(a). We further claim the identification of the Fermi ature and expected low temperature
modulation.
sheet involved in the semimetallic regime. We show how the
expected nodal hybridization modulates this Fermi sheet to asmall pocket compatible with the description from quantum oscillations, and with both the highly
anisotropic magnetoresistance and the isotropic Nernst effect [3], as summarized by the Fig.1(b).
kFARPESpower fit of kFARPESPBE FS sheet at EFARPES
Sketch of the
hypothetical FS at low T[1] G. Nakamoto et al., Journal of the Physical Society of Japan 64, 4834 (1995).
[2] H. Ikeda and K. Miyake, Journal of the Physical Society of Japan 65, 1769 (1996).
[3] U. Stockert et al., PRL 117, 216401 (2016). Y. Inada et al. Phys. B 230, 690 (1997). T.
Terashima et al., PRB 66, 075127 (2002)

47

P05
Laser-induced topological phase transitions in bilayertransition metal dichalcogenides
H. Chono, K. Takasan, and Y. Yanase
Department of Physics, Kyoto University, Japan
Application of laser light can be a powerful tool for changing and controlling properties ofmaterials. In recent years, topological phases in periodically driven systems by laser light havebeen actively investigated. For example, photoinduced quantum anomalous Hall states were theoretically proposed in laser-irradiated graphene [1,2] and the observation of this phenomenon was
experimentally reported very recently [3]. It was also proposed that topological superconductivity
can be induced with laser light in cuprate thin films [4].
Motivated by these situations, in this study, we theoretically investigate the laser-induced topological phase transitions in bilayer transition metal dichalcogenides (TMDs). Focusing on thetransition metal ions, we can see that the TMD s 2H lattice structure is similar to graphene. Theinterlayer hopping of bilayer TMDs corresponds to the nearest hopping in graphene. Analyzing thetight-binding model for laser-irradiated bilayer TMDs with use of the Floquet theory, we show a
topological phase transition in the band structure. We also examine the possibility of laser-induced
topological superconductivity.

[1] T. Oka, and H. Aoki, Phys. Rev. B 79, 081406 (2009).
[2] T. Kitagawa, T. Oka, A. Brataas, L. Fu, and E. Demler, Phys. Rev. B 84, 235108 (2011).
[3] J. W. McIver, B. Schulte, F.-U. Stein, T. Matsuyama, G. Jotzu, G. Meier, and A. Cavalleri,
arXiv:1811.03522[4] K. Takasan, A. Daido, N. Kawakami, and Y. Yanase, Phys. Rev. B 95, 134508 (2017).

48

P06
Local Magnetic Quadrupole Moments in Insulators
A. Daido1, A. Shitade2 and Y. Yanase1
1
Department of Physics, Kyoto University, Japan
2
RIKEN CEMS

Higher order multipole moments are important physical concepts as evident in multipole
expansion of classical electrodynamics and multipole orderings in strongly-correlated electron
systems [1,2]. In particular, magnetic quadrupole moments (MQMs) have recently been
attracting much attention in relationship with the magnetoelectric effect [3-5].
Theoretically, quantum mechanical definition of MQMs is a difficult task. This is because
the positon operator is ill-defined in the Bloch basis, which prevents us from an intuitive
definition. Historically, such a problem also existed for orbital magnetic dipole moments, but
has been resolved by considering a definition through thermodynamics [6]. Accordingly,
recent theoretical work proposed thermodynamic definition of spin and orbital MQMs [7-10].
The obtained Bloch-basis formulas succeeded to clarify the connection between MQMs andthe magnetoelectric effect: In insulators, chemical potential derivative of MQMs are equivalent
to magnetoelectric coefficients. However, physical meaning of the Bloch-basis formulas is not
obvious, since physical quantities should not depend on the chemical potential in insulators.
In this work, we clarify the relationship between the thermodynamic and classicaldefinitions of MQMS, by considering systems with open boundary conditions rather thanperiodic boundary conditions. We illustrate the idea by showing charge movements in
response to spatially modulated magnetic fields.

[1] P. Santini, et al., Rev. Mod. Phys. 81, 807 (2009).
[2] Y. Kuramoto, H. Kusunose, and A. Kiss, J. Phys. Soc. Jpn. 78, 072001 (2009).
[3] C. Ederer and N. A. Spaldin, Phys. Rev. B 76, 214404 (2007).
[4] N. A. Spaldin, M. Fiebig, and M. Mostovoy, J. Phys.:Condense. Matter 20, 434203 (2008).
[5] N. A. Spaldin, et al., Phys. Rev. B 88, 094429 (2013).
[6] J. Shi, G. Vignale, D. Xiao and Q. Nie, Phys. Rev. Lett. 99, 197202 (2007).
[7] Y. Gao, D.Vanderbilt, and D. Xiao, Phys. Rev. B 97, 134423 (2018).
[8] A. Shitade, H. Watanabe, and Y. Yanase, Phys. Rev. B 98, 020407 (2018)[9] Y. Gao and D. Xiao, Phys. Rev. B 98, 060402 (2018).
[10] A. Shitade, A. Daido and Y. Yanase arXiv: 1811.05596.

49

P07
31

P-NMR study of pressure induced semiconductor –semimetal transition in Black Phosphorus
T.Fujii, Y. Akahama, K. Ueda, Y. Nakai, and T. Mito
Graduate School of Material Science, University of Hyogo JapanThe black phosphorus (BP), a layered material of elemental phosphorus, is a semiconductor
with a narrow gap of 0.3 eV. The semiconducting gap of BP is reduced with pressure, and thesemiconductor to semimetal transition occurs around 1.3 GPa [1]. This material has recently
attracted much attention as a promising candidate for a pressure tunable Dirac system [2,3].
However the existence of a Dirac cone has not been experimentally corroborated yet, because
there is little tools that allow one to investigate band structures under pressure.
In this study, we have carried out 31P-NMR measurements on BP at ambient pressure and forthe first time at high pressures. As nuclear spin-lattice relaxation rate 1/T1 is a physical quantity
reflecting the density of states (DOS), we expect to extract information on the gap structure in the
DOS and also the pressure dependence of the gap by measuring the temperature dependence of
1/T1 at different pressures. However, T1 of BP reaches 1.4´104 sec at 77K and ambient pressure.
For such a ling T1, we needed careful measurement to obtain reliable data especially at low
temperature. We have also performed band structure calculation using the local density
approximation (LDA). The comparison with simulations based on DOS models consisting of theband structure obtained from the LDA calculation and an additional impurity band shows that thetemperature dependence of 1/T1 is explained as the sum of components caused by carriers
thermally excited over gaps between the valence and conduction bands and between the valence
and impurity bands. By applying the DOS model to the analysis of the data up to 0.83GPa, weestimated the pressure-induced variation of the gap structure. Moreover we will show
experimental results in the semimetal phase above 1.6 GPa to discuss the possible realization of
Dirac cone like structure.

[1] K. Akiba et al., J. Phys. Soc. Japan 84. 7 (2015).
[2] P. L. Gong et. al., Phys. Rev. B 93, 195434 (2016).
[3] C. Li et al., Phys. Rev. B 95, 125417 (2017).

50

P08
Transitions of topological spin textures
between skyrmion- and hedgehog-lattice states
in cubic chiral magnets MnSi1-xGex
Y. Fujishiro1, N. Kanazawa1, T. Nakajima2, X. Z. Yu2, K. Ohishi3, Y. Kawamura3,
K. Kakurai2,3, T. Arima2,4, H. Mitamura5, A. Miyake5, K. Akiba5, M. Tokunaga5,
A. Matsuo5, K. Kindo5, T. Koretsune6, R. Arita1,2 and Y. Tokura1,2
1

Department of Applied Physics, The University of Tokyo
RIKEN Center for Emergent Matter Science (CEMS)
3
Neutron Science and Technology Center, Comprehensive Research Organization for
Science and Society (CROSS)
4
Department of Advanced Materials Science, The University of Tokyo
5
The Institute for Solid State Physics (ISSP), The University of Tokyo
6
Department of Physics, Tohoku University
2

Topological spin textures such as magnetic skyrmions[1] and spin hedgehogs[2] show
novel emergent phenomena which can be exploited for spintronic functionalities.
Whereas creation or deletion of them have been intensively studied, switching of spin
textures among different topologically-nontrivial classes remain largely unexplored.
We report on the transitions among skyrmion- and hedgehog-lattice states in cubicchiral magnets MnSi1-xGex with variation of lattice constant controlled by Si/Ge
substitution. By combining neutron scattering, Lorentz transmission electron
microscopy and high-field transport measurement, we observe three different
topological spin textures: skyrmion lattice in x = 0-0.25 as well as two distinct hedgehog
lattices in x = 0.3-0.7 and x = 0.8-1, as respectively characterized by large topologicalHall effect.
The emergence of various topological spin states in the chemical-pressure-controlledmaterials suggests a new route for direct manipulation of the spin-texture topology byfacile mechanical method such as pressure.

[1] S. Mühlbauer et al., Science 323, 915 (2009)[2] N. Kanazawa et al., Phys. Rev. Lett. 106,
156603 (2011)

Figure 1: Variation of magnetic
phase diagram in MnSi1-xGex.

51

P09
Topological lightwaves for optical physics
H. Fujita1 , Y. Tada1 , and M. Sato2 ,1 Institute for Solid State Physics, The University of Tokyo, Japan
2 Department of Physics, Ibaraki University Japan
Topology is of paramount importance for modern physics. From electronic band structures tothe rigidity of origami, the concept of topology ubiquitously roles, continuously improving ourunderstanding of the physics of electrons, spins, phonons, and photons.
Topology of photons usually refers to that of photonic band structures in photonic crystals.
How about that of propagating photons, i.e. lasers? In optics, a study of lightwaves with topological nature has developed in the past decades. Those “structured” lasers have been utilized for
microscopes, optical tweezers, laser ablation, laser acceleration, and so on. Unfortunately, opticalphysics, a study of light-matter interaction, has been noninteracting with those developments.
We have been working at the intersection of the optical physics and the structured light
optics [1, 2, 3, 4], proposing potential applications of the topological lightwaves such as opticalvortex, a lightwave carrying orbital angular momentum, and cylindrical vector beam, a laser
with vortical polarization for optical physics. We found that optical vortices would be useful insystematically generating various topological magnetic defects in chiral magnets and in controllingthe nonequilibrium spin texture in an unconventional way.
In this presentation, we particularly focus on our recent works on cylindrical vector beams(CVBs) [3, 4]. Due to their characteristic spatial profile and the focusing property, CVBs allow us
to control the electric and magnetic field components of them in a way impossible for conventionallasers. We show that this unique feature of CVBs potentially has substantial impact on condensedmatter physics. We show that with CVBs, we would be able to measure the Fermi surface ofmagnetic metals, perform high-frequency magnetic resonance study of semiconductors, control“electromagnonic” excitations of multiferroics, and so on. We also demonstrate that CVBs oﬀer aideal building block for designing nonequilibrium states of matters through Floquet engineering.

[1] Hiroyuki Fujita and Masahiro Sato. Ultrafast generation of skyrmionic defects with vortex
beams: Printing laser profiles on magnets. Phys. Rev. B, 95:054421, Feb 2017.
[2] Hiroyuki Fujita and Masahiro Sato. Encoding orbital angular momentum of light in magnets.
Phys. Rev. B, 96:060407, Aug 2017.
[3] Hiroyuki Fujita and Masahiro Sato. Nonequilibrium magnetic oscillation with cylindrical
vector beams. Scientific Reports, 8(1):15738, 2018.
[4] Hiroyuki Fujita, Yasuhiro Tada, and Masahiro Sato. Accessing electromagnetic properties ofmatters with cylindrical vector beams. arXiv: 1811.10617, 2018.

52

P10
Dzyaloshinskii-Moriya interactions in volborthite:magnetic orders and thermal Hall effectShunsuke Furukawa1 and Tsutomu Momoi2,31Department of Physics, The University of Tokyo, Japan
2
Condensed Matter Theory Laboratory, RIKEN, Japan
3
RIKEN Center for Emergent Matter Science (CEMS), Japan
Volborthite Cu3V2O7(OH)2 2H2O offers an interesting example of a highly frustrated quantum
magnet in which ferromagnetic and antiferromagnetic interactions compete on anisotropic
kagome lattices. A recent density functional theory calculation has provided a magnetic model
based on coupled trimers (Fig. 1(a)) [1], which can explain a broad 1/3-magnetization plateau
and possible bimagnon condensation observed experimentally. Here we study the effects of
Dzyaloshinskii-Moriya (DM) interactions in this compound. By means of a strong-coupling
expansion, we derive an effective model in which pseudospin-1/2 moments emerging on
trimers form a network of an anisotropic triangular lattice (Fig. 1(b)). We show that magnon
excitations from the 1/3-plateau (fully polarized pseudospins) feel a Berry curvature due to the
DM interactions, giving rise to a thermal Hall effect. Comparison with experiment poses
constraints on the coupling constants in the effective model. We also analyze magnetic orders
at low temperatures in light of an effective field theory for a quasi-one-dimensional regime.

Figure 1: Schematic diagrams of (a) the microscopic spin-1/2 model and (b) the effective
pseudospin-1/2 model for a single layer of volborthite. In defining DM vectors, every
bond is oriented from left to right, and an arrow (a dot or a cross) indicates the in-plane(out-of-plane) component. A bar on a DM vector indicates π rotation around the x axis.

[1] O. Janson, S. Furukawa, T. Momoi, P. Sindzingre, J. Richter, and K. Held, Phys. Rev. Lett.
117, 037206 (2016).

53

P11
Flat-Band Compound as a Possible Candidate ofTopological Material
I. Hase 1, T. Yanagisawa2 and K. Kawashima1,21National Instituteof Advanced Industrial Science and Technology (AIST), Japan
2
IMRA Materials R&D Co. Ltd., Japan
Flat-band system has been paid much attention because it will emerge many anomalous
properties, such as exact ferromagnetism, superconductivity, quantum Hall effect, and so on[1].
Among them, quantum Hall effect appears as a direct consequence that the band has non-trivial
topological nature. Even fractional quantum Hall effect is predicted for the flat-band system.
However, although many theoretical researches have been conducted on the flat-band model,
almost no compounds have been found to realize this flat-band system even approximately.
By performing ab-initio band calculation, we have recently found that pyrochlore oxides
A2B2O7 (A=Sn,Pb; B=Nb,Ta) have a quasi-flat band at the top of the valence band[2,3]. Thisband comes from the A-s and O’-p orbitals, and the band structure can be approximated byMielke model, which is one of the models having flat-band. Moreover we found that whenholes are doped, these compounds will have ferromagnetic ground state despite having nomagnetic element. We also found that some of the bands of Sn2Nb2O7 and Sn2Ta2O7 are“reversed”, due to the different strength of the spin-orbit interaction.
In this conference, we will present our study for exploring the flat-band compounds which
are potential candidates of topological and/or magnetic material.

Figure 1: (left panel) The top of the valence band of Sn2Nb2O7. (right panel) Corresponding
band structure of the Mielke model. The bold red lines depict the (quasi-) flat band.

[1] Z. Liu, L. Liu and Y. –S. Liu, Chin. Phys. B 23, 077308 (2014), O. Derzhko, J. Richterand M. Maksymenko, Int. J. Mod. Phys. 29, 1530007 (2015).
[2] I. Hase, T. Yanagisawa, Y. Aiura and K. Kawashima, Phys. Rev. Lett. 120, 196401 (2018).
[3] I. Hase, T. Yanagisawa and K. Kawashima, Nanoscale Res. Lett. 13, 63 (2018).

54

P12
Spin-orbit coupled insulator Ba2MgReO6
D. Hirai1 and Z. Hiroi1
1
Institute for Solid State Physics, The University of Tokyo, Japan
Materials with a strong spin-orbit coupling and large electron correlation havereceived great interests in recent years because of their exotic properties including Weyl
semimetals, axion insulators, topological Mott insulators, and multipolar orders [1]. Amongthese spin–orbit-coupled metals and insulators, a material realization of multipolar orders istheoretically proposed in double perovskite compounds with the d1 electronic configuration[2]. Ba2NaOsO6, a representative material in this family, shows an unusual magneticallyordered phase at low temperatures, which is consistent with the theoretical prediction [3,4].
However, a quadrupole ordered phase expected to exist above the magnetic order has not been
experimentally confirmed yet.
Here, we report on the cubic double perovskite Ba2MgReO6 containing Re6+ ions in the 5d1
electron configuration as a promising candidate of the spin-orbit coupled insulator hosting thequadrupolar order. Resistivity, magnetization, and heat capacity measurements using single
crystals show that the compound is a Mott insulator with a magnetic transition at Tm = 18 K
and another transition at Tq = 33 K (Fig. 1b). The significance of spin-orbit coupling isrevealed by the reduced effective magnetic moment of ~0.68 μB at high temperatures above Tq
and the total electronic entropy close to Rln4. These features indicate that Ba2MgReO6 is aspin-orbit coupled Mott insulator possessing a Jeff = 3/2 quartet state, which exhibits
quadrupole and dipole orders at Tq and Tm, respectively.

Figure 1: Temperature depdndence of (a) invserse of magnetic susceptibility and (b) heat capacityof Ba2MgReO6.

[1] W. Witczak-Krempa, et al., Annu. Rev. Condens. Matter Phys. 5, 57 (2014).
[2] G. Chen, R. Pereira, and L. Balents, Phys. Rev. B 82, 174440 (2010).
[3] A. S. Erickson, et al., Phys. Rev. Lett. 99, 016404 (2007).
[4] L. Lu, et al., Nat. Commun. 8, 14407 (2017).

55

P13
Skyrmion formation and enhanced emergent electrodynamics incentrosymmetric magnets
Max Hirschberger1*, Taro Nakajima1*, Shang Gao1, Licong Peng1, Akiko Kikkawa1, Takashi
Kurumaji1‡, Markus Kriener1, Yuichi Yamasaki2,3, Hajime Sagayama4, Hironori Nakao4, Kazuki
Ohishi5, Kazuhisa Kakurai5, Yasujiro Taguchi1, Xiuzhen Yu1, Taka-hisa Arima1,6, and Yoshinori
Tokura1,7
1
RIKEN Center for Emergent Matter Science (CEMS),Wako 351-0198, Japan.
2
Research and Services Division of Materials Data and Integrated System (MaDIS), National
Institute for Materials Science (NIMS), Tsukuba 305-0047, Japan
3
PRESTO, Japan Science and Technology Agency (JST), Kawaguchi 332-0012, Japan
4
Institute of Materials Structure Science, High Energy Accelerator Research Organization,
Tsukuba, Ibaraki 305-0801, Japan
5
Neutron Science and Technology Center, Comprehensive Research Organization for Scienceand Society (CROSS), Tokai, Ibaraki 319-1106, Japan
6
Department of Advanced Materials Science, University of Tokyo, Kashiwa, Chiba 277-8561,
Japan
7
Department of Applied Physics, University of Tokyo, Bunkyo-ku 113-8656, Japan*: equal contribution

Research on magnetic skyrmions, which are nanometric whirls in non-collinear magnets, has long
been focused on non-centrosymmetric compounds (such as the B20 family) or interfaces, where
Dzyaloshinskii-Moriya interactions favor twisted spins structures with fixed helicity.
We report on our recent experimental efforts to study skyrmion formation and associatedtransport responses in centrosymmetric magnets, where DM interactions are absent or cancel out globally,
and where left- and right-handed spirals are nearly degenerate. Here, spiral spin structures are stabilized
by RKKY interactions and the size of a single skyrmion is typically smaller than 3 nm, resulting in a giant
emergent magnetic field detectable by means of the topological Hall effect.

56

P14
Multipolar DM interaction in 5d electron systems
M. Hosoi1 , T. Mizoguchi2 , T. Hinokihara1 , H. Matsuura1 , and M. Ogata1
1 Department of Physics, The University of Tokyo, Japan
2 Graduate School of Pure and Applied Sciences, The University of Tsukuba, JapanThe collaboration between strong spin-orbit coupling and strong electron correlation attracts
much attention due to many physically interesting phenomena. 5d electron systems oﬀer an ideal
arena to investigate this collaboration on account of their strong spin-orbit coupling. Recently, 5d 5electron systems such as iridium based compounds have been enthusiastically studied. Examples
include Sr2 IrO4 , which shows an unconventional metal-insulator transition [1], and Na2 IrO3 , which
is proximity to the Kitaev spin liquid [2]. These materials have the half-filled band of jeﬀ = 1/2
doublet, which is constructed from t2g orbitals with pseudo angular momentum leﬀ = 1.
In contrast to 5d 5 systems, jeﬀ = 3/2 quartet becomes active in 5d 1 systems. Remarkably, notonly dipolar moment, which corresponds to usual spin degree of freedoms, but also higher-rank
multipoles such as quadrupole and octupole become active for 5d 1 systems due to its fourfold
orbital degree of freedom. Indeed, these multipoles induce many exotic phases such as thequadrupolar ordered phase in a double-perovskite material Ba2 NaOsO6 [3].
It is even more interesting if we consider the eﬀects of spacial inversion symmetry breaking(ISB). If the system has magnetic dipole moments, the lack of spacial inversion symmetry induces
anti-symmetric exchange interaction, i.e. the Dzyaloshinskii-Moriya (DM) interaction. For 3d
systems, the DM inrteraction has been evaluated precisely by first principles calculations. On theother hand, for 5d 1 systems, which have the higher-rank multipolar degrees of freedom, we expectthat there exist the analogues of DM interactions for the higher-rank multipoles, which can lead tonovel phases with chiral multipole orders.
In this poster presentation, we study anti-symmetric exchange interactions between multipolar
moments using exact diagonalization method on two-site multiband Hubbard model. We discuss
two types of configuration of octahedron AO6 (A : 5d ion), corner-sharing and edge-sharing
configuration. The corner-sharing figuration appears in perovskite type crystal structure and edgesharing one in hyperkagome or post-perovskite crystal structure. We will show the existence of
DM interaction between the dipoles of jeﬀ = 3/2, as well as between higher-rank multipoles thatconsist of products of jeﬀ -operators for both confugurations.

[1] B. J. Kim, et al., Phys. Rev. Lett. 101, 076402 (2008).
[2] G. Jackeli and G. Khaliullin, Phys. Rev. Lett. 102, 017205 (2009).
[3] G. Chen, R. Pereira, and L. Balents, Phys. Rev. B 82, 174440 (2010).

57

P15
Mechanism of superconductivity in Kondo lattice withsemi-metallic conduction bands
S. Iimura1 , M. Hirayama2 , and S. Hoshino1
1 Department of Physics, Saitama University, Japan
2 RIKEN Center for Emergent Matter Science (CEMS), Japan

Non-local and anisotropic Cooper pairings are usually favored in heavy-electron materials withnearly localized f -electron. On the other hand, the full-gap nature of the superconducting states
in CeCu2 Si2 [1] and UBe13 [2] have been revealed by the specific heat measurements in a rotating
magnetic-field. Therefore it is desirable to propose a new mechanism of superconductivity that is
specific to heavy-electron materials.
Here we theoretically study the Kondo lattice with semi-metallic conduction bands, where
conduction electrons and conduction holes compete in screening the localized spin moment.
Based on the mean-field approach, we reveal that the quantum mechanical superposition between
electron conduction band and hole conduction band is realized through the formation of the Kondosinglet states (Fig.1). The resultant ground state spontaneously breaks the gauge symmetry to makethe system superconducting. This superconducting state is characterized by the composite pairing
amplitude, which has been proposed in the context of two-channel Kondo lattice[3]. We havedemonstrated here that the semi-metallic conduction bands with electron and hole Fermi surfaces
are closely related to the composite pairing. In addition, we discuss the possible application toreal heavy-electron materials.
Kondo singlet withelectron surface
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ff<latexit sha1_base64="LLagMHebbSaRgSA+s0QanM4n3EU=">AAACZHichVHLSsNAFD2Nr1ofrRZBEEQsiqtyI4LiqujGZR+2ClokiVMNTZOQpIVa/AHdKi5cKYiIn+HGH3DRHxDEZQU3LrxNA6JFvcPMnDlzz50zM6pt6K5H1AxJPb19/QPhwcjQ8MhoNDY2XnCtqqOJvGYZlrOtKq4wdFPkPd0zxLbtCKWiGmJLLa+397dqwnF1y9z06rYoVpQDUy/pmuIxlSntxRKUJD9muoEcgASCSFuxW+xiHxY0VFGBgAmPsQEFLrcdyCDYzBXRYM5hpPv7AseIsLbKWYIzFGbLPB7waidgTV63a7q+WuNTDO4OK2cwR090Ry16pHt6oY9fazX8Gm0vdZ7VjlbYe9GTydz7v6oKzx4Ov1R/evZQworvVWfvts+0b6F19LWji1ZuNTvXmKdremX/V9SkB76BWXvTbjIie4kIf4D887m7QWExKVNSziwlUmvBV4QxhVks8HsvI4UNpJHncwVOcYbz0LM0LMWliU6qFAo0cXwLafoT0kyJ5g==</latexit><latexit sha1_base64="LLagMHebbSaRgSA+s0QanM4n3EU=">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</latexit>ei✓| i = p (|"e , #f i2<latexit sha1_base64="/ho6tYNuHP/ueQ2uvCjIRvwnF1M=">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</latexit>e i✓|#e , "f i) + p (|"h , #f i |#h , "f i)2
Kondo singlet with
“Quantum mechanicalelectronbetween
surface |e, f i and |h, f i
superposition”<latexit sha1_base64="IghihBOmjLGq96kdg6Leu/orKOk=">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</latexit><latexit sha1_base64="9/7+4y3up5CEghYx9zFaUVoUa2o=">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</latexit>

Figure 1: Conceptual picture of the mechanism of superconductivity in Kondo lattice with semi-metallic
conduction bands.

[1] S. Kittaka, Y. Aoki, Y. Shimura, T. Sakakibara, S. Seiro, C. Geibel, F. Steglich, H. Ikeda, andK. Machida, Phys. Rev. Lett. 112, 067002 (2014).
[2] Y. Shimizu, S. Kittaka, T. Sakakibara, Y. Haga, E. Yamamoto, H. Amitsuka, Y. Tsutsumi,
and K. Machida, Phys. Rev. Lett. 114, 147002 (2015).
[3] P. Coleman, A. M. Tsvelik, N. Andrei, and H. Y. Kee, Phys. Rev. B 60, 3608 (1999).

58

P16
Supercurrent-induced Edelstein eﬀect
Y. Ikeda, and Y. Yanase
Department of Physics, Kyoto University, Japan
Controlling of magnetic moments using local electric current is an important topic in themodern field of spintronics. One of the representative methods is the Edelstein eﬀect [1], in which
an electrical current generates nonequilibrium spin density through a splitting of the Fermi surface
in noncentrosymmetric metals with strong spin-orbit coupling, e.g. interface Rashba systems[2, 3]. However, for practical applications, e.g. domain rotation and reversible magnetization
switching [4], large amount of current density (7 × 105 [Acm−2 ]) is needed. Therefore, Joule
heating created by dissipative current is a main obstacle for eﬃcient control of magnetization.
In this study, we suppose that the surface state of d-wave superconductors is a good candidate foreﬃcient magnetization control. D-wave superconductors show topologically nontrivial properties[5], and is accompanied by unique surface band structure, e.g. Majorana flat band in its edge
mode [6]. Using theoretical framework for the dissipationless supercurrent [7, 8], we examine thesupercurrent induced Edelstein eﬀect by tight-binding model calculations.

[1] V. M. Edelstein, Solid State Commun. 73 233 (1990)[2] A. Manchon et al, Phys. Rev. B 78, 212405 (2008).
[3] I. M. Miron et al, Nat. Mat. 9, (2010)[4] A. Chernyshov et al, Nat. Phys. 5, (2009)[5] X. L. Qi et al, Rev. Mod. Phys. 13, 1057 (2011)[6] K. Yada et al, Phys. Rev. B 83, 064505 (2011)[7] R. Takashima et al, Phys. Rev. B 94, 235117 (2016)[8] T. Jonckheere et al, J. Phys. Soc. Jpn 87, 094705 (2018)59

Figure 1: Surface states of current flowing
d-wave superconductor

P17
Excitonic condensation in correlated cobaltite LaCoO3 at
ultrahigh magnetic field
A. Ikeda, Y. H Matsuda, D. Nakamura, S. Takeyama and K. Sato1
ISSP Univ. of Tokyo, Kashiwa, Japan
Ibaraki Nat. coll. of Tech.1, Hitachinaka, Japan
In a cobaltite, LaCoO3, the spin-state degree of freedom of Co+3 (d6) varies from high(HS), intermediate and low spin states (LS) with S=0, 1, 2, respectively, due to the balance ofHund's coupling and crystal field splitting. A first order magnetic transition induced bymagnetic field at 60 T is reported [1] from a non-magnetic ground state to a magnetized state,whose origin is still unclear. Besides, by constructing B-T phase diagram, we recently clarified
that the magnetic phase is divided into two phases separated by the temperature of ~30 K [2].
Theories argue that the field induced magnetic phase may be originated in the excitonic
condensation. Those exotic phase appears in cobaltites as a result of the spontaneous
hybridization of LS and HS states [3-5]. In excitonic condensation, the multipole order of spinand orbitals are realized as a result of the interference between different spin states, whichsometimes involves nematicity of spin and orbitals. The field induced phase does not containthe nematicity of spin and orbitals in the ideal limit where spin-orbit interaction is absent
which is not true for the actual cobaltite.
In the present study, we have investigated the high magnetic field phase diagram of
LaCoO3 with magnetostriction measurements. We have developed a high speed
magnetostriction measurement system for detecting the spin-state evolution of LaCoO3 [6]. So
far, we have confirmed that the B-T phase diagram of LaCoO3 constructed by themagnetization measurement is complemented by the magnetostriction measurement.
[1] K. Sato, A. Matsuo, K. Kindo, Y. Kobayashi, and K. Asai, J. Phys. Soc. Jpn. 78, 093702(2009). [2] A. Ikeda, T. Nomura, Y. H. Matsuda, A. Matsuo, K. Kindo, and K. Sato, Phys. Rev. B
93, 220401(R) (2016). [3] T. Tatsuno, E. Mizoguchi, J. Nasu, M. Naka, and S. Ishihara, J. Phys.
Soc. Jpn. 85, 083706 (2016). [4] A. Sotnikov and J. Kuneˇs, Scientific Reports 6, 30510 (2016). [5]
T. Kaneko and Y. Ohta, Phys. Rev. B 90, 245144 (2014). [6] A. Ikeda, T. Nomura, Y. H. Matsuda,
S. Tani, Y. Kobayashi, H. Watanabe, and K. Sato, Rev. Sci. Instrum. 88, 083906 (2017).

60

P18
Magnetic Phases of Non-collinear Antiferromagnet Mn3Sn
M. Ikhlas1 , T. Tomita1 , and S. Nakatsuji1
1 Institute for Solid State Physics, The University of Tokyo, JapanThe metallic antiferromagnet Mn3 Sn with triangular spin structure exhibits large anomalous
Hall eﬀect[1], anomalous Nernst eﬀect[2], and spontaneous magneto-optical Kerr eﬀect[3], comparable to ferromagnets. Conventionally, such behaviors are unexpected in antiferromagnets
with vanishing magnetization. However, it is known that spontaneous oﬀ-diagonal electronic
responses can appear in antiferromagnets whenever the symmetry of the antiferromagnetic structure is equivalent to collinear ferromagnets[4]. The unique electronic properties of the triangularspin structure, combined with the low magnetization and terahertz spin dynamics, make Mn3 Sn apromising material for spintronic devices. In its bulk form, Mn3 Sn single crystals are reported to
be stable within a range of Mn compositions, Mn3+x Sn1−x . Depending on the initial composition
and growth condition, three distinct kinds of magnetic phases can be stabilized as a function oftemperature, namely the high-temperature triangular spin structure phase[5], the intermediate helical phase[6], and the low-temperature cluster spin-glass phase[7]. Here we report the magnetic
phase diagram of Mn3 Sn as a function of Mn composition using magnetization and transport measurements. We found that the helical phase is the intrinsic ground state of Mn3 Sn, and the excess
Mn extends the parameter region of the triangular spin structure on the phase diagram.

[1] S. Nakatsuji, N. Kiyohara and T. Higo, Nature 527, 212-215 (2015).
[2] M. Ikhlas, T. Tomita, T. Koretsune, M.-T. Suzuki, D. Nishio-Hamane, R. Arita, Y. Otani and
S. Nakatsuji, Nature Physics 13, 1085-1090 (2017).
[3] T. Higo., H. Man., D.B. Gopman, L. Wu, T. Koretsune, O.M. van’t Erve, Y.P. Kabanov,
D. Rees, Y. Li„ M.T. Suzuki, S. Patankar, M. Ikhlas, C.L. Chien, R. Arita, R.D. Schull, J.
Orenstein and S. Nakatsuji, Nature Photonics 12, 73-78 (2018)[4] M.-T. Suzuki, T. Koretsune, T. Ochi and R. Arita, Phys. Rev. B 95, 012345 (2017).
[5] T. Nagamiya, S. Tomiyoshi, Y. Yamaguchi, Solid State Commun. B 42, 385-388 (1982).
[6] J.W. Cable, N. Wakabayashi, P. Radhakrishna, Solid State Commun. B 88, 161-166 (1983).
[7] W. J Feng, D. Li, W. J Ren, Y.B. Li, W. F. Li, J. Li, Y. Q. Zhang and Z. D. Zhang, Phys. Rev.
B 73, 205105 (2006.

61

P19
Rectification of Spin Current in Magnetic Insulatorswith Linearly-Polarized Electromagnetic Waves
Hiroaki Ishizuka1 and Masahiro Sato2
1
Department of Applied Physics, The University of Tokyo, Japan2
Department of Physics, Ibaraki University, Japan
Manipulation of magnetic states and spin current is a key subject in spintronics [1]. In
conductive materials, the charge current is often used for such purposes; magnetic domain
walls are moved by spin-transfer effect and spin Hall effects are used to generate spin current.
The concept of spintronics is also applied to magnetic insulators, which have several
advantages over the conductive materials: Magnetic excitations typically have a longer lifetimeand no ohmic loss in the insulators. A technical challenge, however, exists in controlling themagnetic excitations which carry the angular momentum in the magnetic insulators;
manipulating the magnetic excitations are not as easy as electrons because they are chargeless.
Recent studies on opto-spintronics found that electromagnetic waves are a useful tool forcontrolling the magnetic states. On the other hand, the method for manipulating spin current inmagnetic insulators is limited to ferromagnets, i.e., by spin pumping.
In this work, we explore a method for generating dc spin current in antiferromagnetic
insulators (Fig. 1). By considering a noncentrosymmetric spin chain, we theoretically showthat a dc spin current is induced by a linearly-polarized electromagnetic wave [2]. In particular,
we find that three coupling terms between
the spins and electromagnetic waves giverise to the spin current: Inverse
Dzyaloshinskii-Moriya,
Zeeman,andmagnetostriction couplings. The richmicroscopic mechanisms are reflected in
the anisotropy and frequency dependenceof the induced spin current. We discussthat the spin current is a consequence ofthe non-trivial shift of magnetic excitations
during the quantum transition by the
Figure 1: The setup we consider in our theory. The
electromagnetic wave. This spin current
model we consider applies to (a) 1d spin chain as
potentially provides a method for fast
well as (b) to a weakly coupled spin chain.
control of spin current in antiferromagnets.
[1] Spin Current, edited by S. Maekawa, S. O. Valenzuela, E. Saitoh, and T. Kimura (Oxford
University Press, Oxford, England, 2012).
[2] H. Ishizuka and M. Sato, submitted.

62

P20
NQR Study of Multipole orders in PrT2Al20 (T=Ti, V)
T. Isomae, H. Takeda, M. Takigawa, A. Sakai, S. Nakatsuji
Institute for Solid State Physics, University of Tokyo, Japan
Materials containing non-kramers Pr3+ ions provide a rich research field on multipole
physics in f-electron systems, of which PrT2Al20 (T=Ti,V), are promising candidate. They havenon-magnetic Γ3 doublet ground state in the cubic crystaline electric field with zero magnetic
dipole but finite electric quadrupole and magnetic octupole moments. A 3z2-r2 type ferroquarupole order occurs in PrTi2Al20 at 2 K with concomitant switching of quadrupole orderparameter in magnetic fields as discovered by the recent NMR experiment [1]. On the other
hand, PrV2Al20 with stronger c-f hybridization exhibits
more complex phenomena, such as non-Fermi liquidbehavior suggestive of quadrupole Kondo effects, double
phase transitions in temperature, and magnetic-fieldinduced phase transitions.
Here we present results of 27Al-NQR measurements
on single crystals of PrT2Al20 (T=Ti, V) to detect
symmetry breaking and fluctuations associated withmultipole order. Breaking of crystalline symmetry due toferro-quadrupole order in PrTi2Al20 has been detected as
NMR line splitting caused by anisotropic hyperfine fieldin magnetic fields [2]. We are now trying to detect
symmetry lowering of the electric field gradient by zerofield NQR. In PrV2Al20 possible octupole order, as has
been theoretically considered [3], may generatespontaneous hyperfine magnetic field even at zero field.
The right figure shows the temperature dependence of
NQR frequency and the line width at the Al(3) sites in
PrV2Al20. Although there is no change in the NQR
frequency, the line width increases gradually below 1K.
Temperature dependence of NQR
frequency and the line width[1] T. Taniguchi et al., in preparation.
[2] T. Taniguchi et al., J. Phys. Soc. Jpn. 85 (2017) 113703.
[3] F. Freyer et. al., Phys. Rev. B 97 (2018) 115111.

63

P21
Anomalous Zeeman effectin strongly spin-orbit coupled systems
Y. Izaki and Y. Fuseya
Dept. Eng. Sci, U. Electro-Communications, Japan
Topological materials exhibit specific properties which cannot be classified by the

M(=Ez/Ec)

conventional band theory. Recently, a lot of experiments and theories on the topologicalmaterials, such as topological insulators and Weyl semimetals, were reported. Many topologicalmaterials possess the Dirac electrons (or Weyl electrons), which have linear dispersions. One of
the typical way to judge the existence of Dirac electrons to observe the linear dispersion by the
ARPES measurements or by the first principles calculation. However, the linear dispersions do
not grantee the existence of Dirac electros. In order to evaluate how the electrons in crystals areclose to the “true” Dirac electrons --- “Diracness”---, it would be most useful to measure or
calculate a ratio of the Zeeman splitting to the cyclotron energy (M=Ez/Ec)[1]. Experimentally,
the ratio M can be determined by the measurement of quantum oscillations. Theoretically, M cabe determined by calculating the energy levels under a magnetic field. In principle, the energy
levels under a magnetic field can be precisely calculated based on the k.p theory as was shown
by Luttinger and Kohn [2]. In practice, however, it is too complex to calculate the energy levelsof a specific solid because of the noncommutativity of the kinematical momentum operator π(=p-eA), which does not allow us to use the simple diagonalization technique. Even today, theenergy levels under the magnetic field for multiband system can be obtained perturbatively
using the Löwdin partitioning [3]. In this
0.85
study, we introduce a new numerical
0.8
technique to calculate the energy levels
0.75
under the magnetic field exactly by
0.7
considering the noncommutativity of π. By
0.65
using this technique, we show that the ratio
0.6
M, which has been believed to be
0.55
independent from the magnetic field, exhibita remarkable field dependence as shown in
0.5
0
5
10
15
20
25
30
Figure 1.
B(T)Figure 1 : Magnetic Field dependence of M

[1] H. Hayasaka and Y. Fuseya, J. Phys. :Condens.Matter 28,31LT01 (2016)[2] J. M. Luttinger and W. Kohn, Phys. Rev. 97, 869 (1955)[3] Y. Fuseya, et al, Phys. Rev. Lett. 115, 216401(2015)

64

P22
Coupled Spin-Charge Fluctuation in the Semimetal Phaseof All-In/All-Out Antiferromagnet Cd2Os2O7
A. Koda1,2 , H. Hirose3,† , M. Miyazaki1,§ , H. Okabe1 , M. Hiraishi1 , I. Yamauchi1,‡ ,K. M. Kojima1,2,¶ , J. Yamaura3,∗ , Z. Hiroi3 , and R. Kadono1,2
1 Muon Science Laboratory and Condensed Matter Research Center, Institute ofMaterials Structure Science, High Energy Accelerator Research Organization (KEK),
Tsukuba, Ibaraki 305-0801, Japan
2 Department of Materials Structure Science, SOKENDAI, Japan
3 Institute for Solid State Physics, University of Tokyo, Kashiwa, Chiba 277-8581, Japan

It is inferred from muon spin rotation experiment that the all-in/all-out osmium spin structure
realized in the antiferromagnetic phase of a pyrochlore compound Cd2 Os2 O7 (with the Néel temperature TN ≃ 227 K) serves as a stage of novel electromagnetic fluctuation over the temperature
range between T ∗ ≃ 150 K and TN , where T ∗ marks the Lifshitz transition between semiconductor(T < T ∗ ) and semimetal (T > T ∗ ) phases[1]. Strong muon depolarization observed upon substitution of Os (5d 3 ) with small amount of Re (5d 2 ) [Cd2 (Os1−x Re x )2 O7 with x = 0.01–0.03] indicatesthat the magnetic fluctuation is coupled with the mobile holes in the semiconductor phase, which
is drastically enhanced by intrinsic carriers in the semimetal phase. Remarkably, the relevant spincharge dynamics is hidden to other magnetic probes such as magnetic susceptibility[2], NMR[3],and resonant x-ray diﬀraction[4], demonstrating its unique time scale of 10−7 to 10−10 s−1 with asoliton-like character of propagation associated with the Ising-like local anisotropy.

[1] C. H. Sohn et al., Phys. Rev. Lett. 115, 266402 (2015).
[2] A. Sleight et al., Solid State Commun. 14, 357 (1974).
[3] I. Yamauchi et al., Phys. Soc. Jpn. 2011 Autumn Meeting, unpublished.
[4] J. Yamaura et al., Phys. Rev. Lett. 108, 247205 (2012).

†Present address: National Institute for Materials Science, Tsukuba, Ibaraki 305-0003, Japan§Present address: Muroran Institute of Technology, Muroran, Hokkaido 050-8585, Japan‡Present address: Graduate School of Science and Engineering, Saga University, Saga 840-8502, Japan¶Present address: Centre for Molecular and Materials Science, TRIUMF, Vancouver, BC V6T2A3, Canada∗Present address: Materials Resarch Center of Element Strategy, Tokyo Institute of Technology, Japan

65

P23
Spin-orbit-coupled ferroelectric superconductivity andmultiorbital effects in doped SrTiO3
S. Kanasugi and Y. Yanase
Department of Physics, Kyoto University, Japan
SrTiO3 (STO) is a rare example of a system in which superconductivity and dielectricity isclosely related. The quantum paraelectric STO exists in the vicinity of a ferroelectric (FE)quantum critical point[1]. Therefore, STO becomes a FE by chemical substitution orapplication of stress. On the other hand, slightly doped STO exhibits metallic behavior withsuperconducting instability at low temperatures[2]. The pairing mechanism of superconducting
STO is a long-standing problem of the condensed matter physics, since it occurs in an
exceptionally low carrier density region where the Migdal-Eliashberg approximation is not
appropriate. Although the FE quantum criticality and superconductivity in STO have been
considered to be unrelated for a long time, their close correlations are pointed out these days[3].
For example, a coexistent phase of FE-like order and superconductivity, namely FE
superconducting phase, have been discovered in Ca-substituted and carrier doped STO[4].
Motivated by recent studies about the correlation between FE quantum criticality andsuperconductivity in STO, we investigated the stability of the FE superconducting phase byusing a multiorbital model for bulk STO[5]. Since FE phase transition breaks the inversion
symmetry and induces antisymmetric spin-orbit coupling (ASOC), we assumed a proportional
relationship between the FE order parameter and the strength of ASOC[6]. It is shown that the
FE superconducting phase is stabilized even though the normal state is paraelectric. We willshow that the stabilization of the FE superconducting phase is caused by the Lifshitz transition
induced by the ferroelectricity. In addition, it is demonstrated that the upper critical field of the
FE superconducting phase is drastically enhanced thanks to the ASOC and multiorbital effect.

[1] S. E. Rowley et al., Nat. Phys. 10, 367-372 (2014).
[2] X. Lin et al., Phys. Rev. X 3, 021002 (2013).
[3] J. M. Edge et al., Phys. Rev. Lett. 115, 247002 (2015).
[4] C. W. Rischau et al., Nat. Phys. 13, 643-648 (2017).
[5] Y. Nakamura and Y. Yanase, J. Phys. Soc. Jpn. 82, 083705 (2013).
[6] S. Kanasugi and Y. Yanase, Phys. Rev. B 98, 024521 (2018).

66

P24
Enhanced Thermopower in Hole-doped Pyrochlore
Iridates with Quadratic Band Touching
R. Kaneko1, M-T. Huebsch2, S. Sakai2, R. Arita1,2, H. Shinaoka3, K. Ueda1, Y. Tokura1,2
and J. Fujioka1,4,5
1 Department of Applied Physics, University of Tokyo, Japan
2 RIKEN Center for Emergent Matter Science (CEMS), Japan
3 Department of Physics, Saitama University, Japan
4 Graduate School of Pure and Applied Sciences, niversity of Tsukuba, Japan
5 PRESTO, Japan Science and Technology Agency, Japan

Quadratic band touching (QBT) is a band structure in which the parabolic valence
and conduction band touch at a point, protected by spatial and time inversion
symmetry. The possibility that QBT becomes the source of exotic electronic phasessuch as Weyl semimetal has been discussed. The existence of QBT has been
confirmed in Pr2Ir2O7 (PIO)[1], which is a member of pyrochlore-type iridate R2Ir2O7(RIO, R=Rare earth). Since QBT in PIO is stabilized by the crystal symmetry, we canconsider the possibility of the universal existence of QBT in the paramagnetic
metallic phase of RIO. Therefore, we made hole-doped samples of insulator Eu2Ir2O7
to compare its electronic properties with PIO.
Using the transport measurement and ab-initio calculation, we have explored thethermopower and electronic structure of correlated metal with QBT in hole-doped
pyrochlore iridates. We found that the hole-doped QBT yields a thermopower peak,which can be enhanced exceeding 40
V/K below 50 K by tuning the bandfilling and lattice distortion. The
thermopower peak is observed even in
the doping induced metallic phasecreated

from

Mott

insulator,

indicating that the QBT is robust
against the strong electron correlation
as well as the lattice distortion while
keeping the cubic symmetry.
[1] T. Kondo et al., Nat. Commun. 6,

Fig.

10042 (2015)transport property of (R1-xCax)2Ir2O7

67

Phase

diagramandrepresentativeP25
Assessing the numerical accuracy of tensor-network
representation of the Kitaev spin liquid
R. Kaneko1 , T. Okubo2 , H.-Y. Lee1 , Y. Yamaji3 , and N. Kawashima1
1 Institute for Solid State Physics, The University of Tokyo, Japan
2 Department of Physics, The University of Tokyo, Japan
3 Department of Applied Physics, The University of Tokyo, JapanThe Kitaev honeycomb model is one of the rare two-dimensional integrable systems in which
the ground state is a spin liquid [1]. Iridium and ruthenium compounds are promising candidates
for realizing the Kitaev model [2, 3]. However, the effective models of real compounds may
deviate from the original Kitaev model and include additional spin exchange interactions that
could stabilize magnetic order at low temperatures [4–6]. General-purpose numerical methods
are needed for investigating the phase diagram of the generalized Kitaev-like model where theHeisenberg and off-diagonal exchange interactions are present.
To this end, we focus on the tensor-network method in two-dimensional systems and investigate
its applicability to the simplest isotropic ferromagnetic Kitaev model. In particular, we use thetensor product state (TPS) or the projected entangled-pair state (PEPS), which is described in
the spin degrees of freedom, as a variational wave function and obtain the ground state in thethermodynamic limit by imaginary time evolution (ITE). In the previous study, a higher-cost
ITE (full update) was thought to be indispensable [7]; however, this requires at least O(D10 )computational cost with D being a bond dimension for optimization. By contrast, we have foundthat a lower-cost ITE (simple update), which only requires O(D5 ) cost, is sufficient to represent
the gapless spin liquid when the initial TPS is carefully chosen according to the required physicalsymmetries as well as the zero-flux configuration of the Z2 gauge field. We discuss how toconstruct such an optimal TPS for D = 2 and how the energy is improved as D is increased. We
also report the stability of spin liquid obtained by numerical optimization against perturbations
such as the Heisenberg exchange interaction and the magnetic field.

[1] A. Kitaev, Ann. Phys. (NY) 321, 2 (2006).
[2] J. Chaloupka, G. Jackeli, and G. Khaliullin, Phys. Rev. Lett. 105, 027204 (2010).
[3] J. Chaloupka, G. Jackeli, and G. Khaliullin, Phys. Rev. Lett. 110, 097204 (2013).
[4] X. Liu, T. Berlijn, W.-G. Yin, W. Ku, A. Tsvelik, Y.-J. Kim, H. Gretarsson, Y. Singh, P.
Gegenwart, and J. P. Hill, Phys. Rev. B 83, 220403(R) (2011).
[5] Y. Singh and P. Gegenwart, Phys. Rev. B 82, 064412 (2010).
[6] Y. Singh, S. Manni, J. Reuther, T. Berlijn, R. Thomale, W. Ku, S. Trebst, and P. Gegenwart,
Phys. Rev. Lett. 108, 127203 (2012).
[7] J. O. Iregui, P. Corboz, and M. Troyer, Phys. Rev. B 90, 195102 (2014).

68

P26
Rashba-Dresselhaus eﬀect in magnetic insulators
M. Kawano1 , Y. Onose2 , and C. Hotta1
1 Department of Bacis Science, University of Tokyo, Japan
2 Institute for Materials Research, Tohoku University, Japan
In electronic systems, the spin-orbit coupling induces a spin and a momentum dependent band
splitting called Rashba-Dresselhaus eﬀect. So far, this kind of phenomena were rarely observedin magnetic insulators, although their low energy excitations are governed by magnons carrying aspin momentum. Few cases show magnon band splitting[1] and spin textures in momentum spaceis theoretically proposed but only in a rather unrealistic situation[2]. This is because the SU (2)spin degrees of freedom in electrons that can couple to orbital motions is not present in usual
magnets. Here, we show that the inversion-symmetry broken two-sublattice antiferromagnets canovercome this issue in a natural manner by making use of the two-sublattice degrees of freedom
as pseudo-spins[3]. We construct the SU (2) degrees of freedom within the product space ofthe particle-hole and two-sublattice degrees of freedom, and find that the Dzyaloshinskii-Moriya
interaction (DMI) couples the pseudo-spin and space motions of magnons and generates a magnon
band splitting and spin textures in momentum space(Fig.1), which are regarded as the RashbaDresselhaus eﬀect of magnons. We also classify a role of the DMI, and present a systematic way
to design spin textures in momentum space.

(a)

(b)
1.20

1

1

1.05
0.90
0.75

0

0

0.60
0.45
0.30
0.15

-1

-1
-1

0

-1

1

0

1

Figure 1: (a) Rashba-type and (b) Dresselhaus-type spin texture of a lower magnon band over the first
Brillouin zone.

[1] R. Cheng, M. W. Daniels, J. -G. Zhu and D. Xiao, Sci. Rep. 6, 24223 (2016), S. Hayami,
H. Kusunose, Y. Motome, J. Phys. Soc. Jpn. 85, 053705 (2016), G. Gitgeatpong, Y. Zhao, P.
Piyawongwatthana, Y. Qiu, L. W. Harriger, N. P. Butch, T. J. Sato, and K. Matan, Phys. Rev.
Lett. 119, 047201 (2017).
[2] N. Okuma, Phys. Rev. Lett. 119, 107205 (2017).
[3] M. Kawano, Y. Onose and C. Hotta, arXiv:1805.03925.

69

P27
Field-orientation effect on the hidden-order transition
in URu2Si2
S. Kittaka1, Y. Haga2, E. Yamamoto2, Y. Onuki3 and T. Sakakibara1
1
Institute for Solid State Physics, The University of Tokyo, Japan
2
Advanced Science Research Center, Japan Atomic Energy Agency, Japan3
Department of Physics, University of the Ryukyus, JapanThe mechanism of a hidden-order transition in URu2Si2 [1] is a long-standing mystery incondensed-matter physics. At the transition temperature TO (~17.5 K), the specific heat showsa sharp jump [2] and the Ising-like moment along the easy c axis shows a kink [3],demonstrating that it is a second-order transition. However, no clear symmetry breaking has
been found at TO in spite of a great amount of experimental and theoretical studies. The natureof the hidden-order phase is also important to uncover the pairing mechanism of
unconventional superconductivity occurring below 1.4 K, whose gap symmetry is likely to be achiral d-wave type [4]. Recently, a possibility of tetragonal symmetry breaking in the hiddenorder phase has been proposed on the basis of the results of magnetic torque, cyclotron
resonance, and X-ray diffraction measurements [5, 6], and is still under intense debate.
In order to obtain further evidence for the tetragonal symmetry breaking in the hiddenorder phase, specific-heat measurements would be powerful because it shows a very sharptransition at TO. To examine the in-plane rotational symmetry, however, precise control of themagnetic-field orientation might be essential because URu2Si2 has an Ising-like anisotropy. In
this study, we have developed a home-built calorimeter [7] whose addendum is fixed strictly inorder to prevent the sample from tilting by strong magnetic torque, and first investigated thefield-angle dependence of TO under a magnetic field rotated within the ac plane. Then, we
found a cosine-like function in its field-angle dependence. In future work, we will examine thebreaking of tetragonal symmetry of the hidden-order transition via specific-heat measurements
under a rotating magnetic field which is precisely applied along the ab plane by means of thiscosine-like out-of-plane anisotropy.

[1] J. A. Mydosh and P. M. Oppeneer, Rev. Mod. Phys. 83, 1301 (2011).
[2] T. T. M. Palstra et al., Phys. Rev. Lett. 55, 2727 (1985).
[3] T. Sakakibara and H. Amitsuka, JJAP Series 8, 240 (1993).
[4] S. Kittaka et al., J. Phys. Soc. Jpn. 85, 033704 (2016).
[5] T. Shibauchi, H. Ikeda and Y. Matsuda, Philos. Mag. 94, 3747 (2014).
[6] S. Tonegawa et al., Nat. Commun. 5, 4188 (2014).
[7] S. Kittaka et al., J. Phys. Soc. Jpn. 87, 073601 (2018).

70

P28
Synthesis and magnetic transport properties ofantiferromagnet MnX (X = Sn, Ge) thin films
A. Kobayashi1 , T. Higo1 , D. Qu1 , S. Nakatsuji1,2 and Y. Otani1,2,3
1
Institute for Solid State Physics, The University of Tokyo, Japan
2
JST CREST, Japan
3
RIKEN-CEMS, Japan
Antiferromagneic materials have recently attracted much attention as the next generation
spintronic device in surge of demand for higher integration density and faster data processing
devices. The advantages of antiferromagnets are such as negligible stray field and highfrequency magnetization dynamics [1]. However, it is difficult to electrically detect orexternally manipulate the Neel state because of the absence of magnetization in these materials.
On the other hand, recently, surprisingly large spontaneous transverse responses have beenfound in noncollinear kagome-lattice antiferromagnets D019 Mn3 X (X = Sn, Ge). They exhibit
large anomalous Hall [2-5], anomalous Nernst [6], and magnetic optical Kerr effects [7] atroom temperature. Not only for bulk crystal systems, but Mn3 Sn thin film has also been
confirmed to show the similar large responses [8], which shall make a significant progress indeveloping functional antiferromagnetic devices.
Here we tried the synthesis of D019 Mn3 X (X = Sn, Ge) thin films by DC-magnetron
sputtering for different composition at various temperatures including room temperature. The
magnetic transport properties such as anomalous Hall, Nernst effect will be reported.

[1] T.Jungwirth et al., Nat. Nanotech. 5, 231 (2016).
[2] H. Chen et al., Phys. Rev. Lett. 112, 017205 (2014).
[3] S. Nakatsuji, N. Kiyohara, and T. Higo. Nature 527, 212(2015).
[4] N. Kiyohara, T. Tomita, and S. Nakatsuji. Phys. Rev. Applied 5, 064009 (2016).
[5] A.K. Nayak et al., Nat. Mater. 16, 1090 (2017).
[6] M. Ikhlas et al., Nat. Phys. 13, 1085 (2017).
[7] T. Higo et al., Nat. Photonics. 12, 73 (2018).
[7] T. Higo, D. Qu, Y. Li, C.L. Chien, Y. Otani and S. Nakatsuji. Appl. Phys. Lett. 113,202402 (2018).

71

P29
Z2 topological invariant for magnon spin Hall systems
H. Kondo, Y. Akagi, and H. Katsura
Department of Physics, The University of Tokyo, JapanThe classification and characterization of different phases of matter based on the topologyof band structures has recently attracted considerable attention. The successful studies on the
topological phenomena of electrons have been extended to bosonic systems. However, thetopological invariant of bosonic systems with time reversal symmetry has not been identified
because Kramers' theorem cannot be directly applied to them.
We introduce the pseudo-time-reversal operator which ensures the existence of ``Kramers
pairs'' of bosons and define the Z2 topological invariant for magnon spin Hall systems [1]. The
topological invariant is defined by using the Berry connection and curvature which are
different from those of electrons [2]. Furthermore, we propose two models of magnon spin
Hall systems, kagome- (Figure 1) and honeycomb- (Figure 2) bilayer systems. The second
system is the first example of magnon spin Hall systems without spin conservation. We
numerically calculate the Z2 topological invariant of these systems and obtain the results which
are consistent with the existence of edge states.

Figure 1: (a) The kagome-bilayer system. (b) Band

Figure 2: (a) The honeycomb-bilayer system. (b) Band

structure in a strip geometry.

structure in a strip geometry.

[1] H. Kondo, Y. Akagi and H. Katsura, arXiv:1808.09149.
[2] R. Matsumoto, R. Shindou, and S. Murakami, Phys. Rev. B 89, 054420 (2014).

72

P30
Impact of antiferromagnetic order on Landau level splittingof quasi-two-dimensional Dirac fermions in EuMnBi2
H. Masuda1, H. Sakai2,3, M. Tokunaga4, M. Ochi2, H. Takahashi1,
K. Akiba5, A. Miyake4, K. Kuroki2, Y. Tokura1,6, S. Ishiwata1,3
1Department of Applied Physics, The University of Tokyo, Japan2
Department of Physics, Osaka University, Japan
3
JST-PRESTO, Japan
4
Institute for Solid State Physics, The University of Tokyo, Japan
5
Department of Physics, Okayama University, Japan
6
RIKEN-CEMS, Japan
Dirac fermions in solids have been of current interest for their unique transport properties. Theinterplay of Dirac fermion with magnetism in magnetic Dirac materials is recently of particularinterest. Among them, EuMnBi2 is a rare compound that exhibits quantum transport of Diracfermions coupled with the field tunable magnetic order[1]. However, it remains elusive how and towhat extent the Dirac-like band dispersion is affected.
In this study, we report spin-split Landau levels of quasi-two-dimensional Dirac fermions in
EuMnBi2, as revealed by interlayer resistivity

100

measurements in a tilted magnetic field up to ~65.0°
63.5°
60.0°
55.0°
50.0°
42.2°
40.0°
60
35.0° H
H
30.0°
25.0°
40
20.0°
18.2°
20
2
3 1.1°
1.4 K – 1.9 K
N = 1.5 2.5spin-flop (H > Hf)
060
22.5 3 3.5 4
50
θ c
40
1.5
40
30
30
20
20
10
10
0
2
3
4
5

Zeeman-to-cyclotron energy ratio. The effective
g-factor estimated from the tilt angle, where theSdH oscillation exhibits a phase inversion,differs by approximately 50% between twophases.

This

observation
θ (deg)signifies a marked impact of the magnetic orderof Eu sublattice on the Dirac-like band structure.
The origin may be sought in strong exchange
coupling with the local Eu moments, as verified
by the first-principles calculation[2].
[1] H. Masuda, H. Sakai et al., Science
Advances 2, e1501117 (2016).

-1-1changing the tilt angle of the field, i.e., the-1-1σzz (Ω cm )interlayer resistivity is strongly modulated byσzz (Ω cm )80

35 T. As shown in Fig. 1, the amplitude of
Shubnikov-de Haas (SdH) oscillation in

antiferromagnetic

3.54

Fig. 1 (a) interlayer conductivity σzz as afunction of HF0/H, normalized inverse outof-plane magnetic field. (b) Image plot of σzz.

[2] H. Masuda, H. Sakai et al., Phys. Rev. B 98,
161108(R) (2018).

73

P31
Pressure-tuning of the interplay between ferroquadrupoleorder and superconductivity in PrTi2Al20
K. Matsubayashi1, F. Motoyama1, R. Hoshi1, N. Sokabe2, T. Isomae2, M. Tsujimoto2,
A. Sakai2, S. Nakatsuji2, S. Kittaka2, Y. Uwatoko2, K. Kitagawa3
1Graduate School of Informatics and Engineering, The University of ElectroCommunications, Japan
2 Institute for Solid State Physics, The University of Tokyo, Japan
3 Department of Physics, The University of Tokyo, Japan
PrTi2Al20 with non-Kramers Γ3 doublet ground state provides an interesting opportunity toinvestigate the interplay between the ferroquadrupole order and superconductivity [1,2]. In
particular, we previously reported that PrTi2Al20 exhibits the enhancement of superconducting
transition temperature near the putative quantum critical point of the ferroquadrupole order at
PC ~ 11 GPa, suggesting that quadrupole fluctuations may provide a nonmagnetic glue for
Cooper pairing. Another peculiar aspect of PrTi2Al20 is that the non-Fermi liquid (NFL)behavior spans even far away from PC coinciding with the robust superconducting phase. We
found that the NFL state emerges not only under pressure but also in wide magnetic field range,
where the resistivity curves are shown to collapse onto a single scaling function, as predicted
for the quadrupole Kondo lattice model [3]. In this presentation, we show the complete highpressure phase diagram of possible quadrupole Kondo lattice system PrTi2Al20 and discusspossible exotic superconductivity in the vicinity of an orbital instability.
[1] A. Sakai et al., J. Phys. Soc. Jpn. 81, 083702 (2012).
[2] K. Matsubayashi et al., Phys. Rev. Lett. 109, 187004 (2012).
[3] A. Tsuruta and K. Miyake, J. Phys. Soc. Jpn. 84, 114714 (2015).

74

P32
Terahertz anomalous Hall effect in Weyl antiferromagnet
Mn3Sn thin film
Takuya Matsuda1, Natsuki Kanda1, Tomoya Higo1,2, N. Peter Armitage3,
Satoru Nakatsuji1,2 and Ryusuke Matsunaga1,41Institute for Solid State Physics, The University of Tokyo, Japan
2
CREST, Japan Science and Technology Agency (JST), Japan3
Department of Physics and Astronomy, The Johns Hopkins University, USA
4
PRESTO, Japan Science and Technology Agency (JST), Japan
Recently Mn3Sn has attracted a great deal of attention as a candidate for the Weyl
semimetal due to breaking of time reversal symmetry in the non-collinear antiferromagnetic
order. One of the most prominent features of this material is that it exhibits giant anomalous
Hall effect at room temperature in spite of vanishingly-small net magnetization [1]. In order todiscuss intrinsic nature of the anomalous Hall effect originating from large Berry curvature in
momentum space, terahertz spectroscopy is important since Mn3Sn has Weyl points very close
to the Fermi energy and therefore peculiar terahertz Hall conductivity may appear as resonant
structures due to interband transition across the band-crossing point [2].
Here, we report terahertz time-domain spectroscopy for Mn3Sn thin films with randomlyoriented magnetic domains. The measurement is performed at zero magnetic field after the
samples are fully magnetized under the field of ±5 T. To obtain the optical Hall conductivity
σxy(ω) in the terahertz frequency range, we built up a broadband terahertz polarization-resolved
spectroscopy setup between 0.2 to 7 THz (0.8 to 28 meV), and measured the polarization
rotation of terahertz electric field in the thin films. Conventional terahertz transmission
spectroscopy provides a Drude-like response in the longitudinal optical conductivity σxx(ω).
Then, we also observed the rotation angle ~4 mrad in the 50-nm-thick film and its sign reversal
when the opposite magnetic field is applied before the terahertz experiment. The result
corresponds to the optical Hall conductivity σxy(ω)~20 Ω-1cm-1 at room temperature, which isconsistent with the giant anomalous Hall effect in the DC resistivity measurement. Observationof the terahertz anomalous Hall conductivity in picosecond time resolution will be extended
into the study of nonequilibrium dynamics of the Weyl antiferromagnetic system excited by
optical pump or intense terahertz electromagnetic excitation.

[1] S. Nakatsuji et al., Nature 527, 212 (2015).
[2] R. Shimano et al., EPL 95, 17002 (2011).

75

P33
Band-tuning-induced giant topological Hall effect inmagnetic semimetal α-EuP3
A. H. Mayo1, H. Takahashi1, A. Nomoto1, H. Masuda1,
H. Sakai2,3, M. S. Bahramy1 and S. Ishiwata1,3
1Department of Applied Physics, The University of Tokyo, Japan2
Department of Physics, Osaka University, Japan
3
JST-PRESTO, Japan

Black phosphorus (BP), a material consisting of monoatomic phosphorene layers stacked
via van der Waals bonding, is a narrow-gap semiconductor in ambient pressure. It has recently
been predicted that BP goes under a topological transition by applying high pressure, resulting
in a semimetallic band structure[1].
α-EuP3 has a crystal structure closely related to BP and contains magnetic Eu2+ ions
between the P layers (Fig.1). Recent first principle calculations predict that semimetallic band
structures originating from the p-orbital of phosphorus are realized in α-CaP3 and α-SrP3,
which are isostructural crystals of α-EuP3[2]. Therefore, we expect the emergence of nontrivial electronic transport derived from the correlation between magnetism and thesemimetallic electronic structure.
So far, we have observed the anomalous Hall effect,
which emerges at a certain value of magnetization(Fig.2). This suggests that the magnetically tuned band
structure plays an important role. In this poster
presentation, I will discuss the correlation between the
band’s exchange splitting and the electronic transport
properties, and also the possibility of a topological originof the anomaly.

Figure 1: Crystal structure of α-EuP3.

Figure 2: Anomalous Hall effect in α-EuP3
occuring at a certain value of magnetazation.

[1] Z. J. Xiang, et. al., Phys. Rev. Lett. 115, 186403 (2015).
[2] Q. Xu, et. al., Phys. Rev. B 95, 045316 (2017).

76

P34
Large Topological Responses in the Antiferromagnet Mn3Ge
T. Chen1, T. Tomita1,2 and S. Nakatsuji1,2
12

Institute for Solid State Physics, University of Tokyo, Kashiwa 277-8581, Japan
CREST, Japan Science and Technology Agency (JST), 4-1-8 Honcho Kawaguchi,
Saitama 332-0012, Japan

Conventionally, intrinsic anomalous Nernst effect has been investigated inferromagnets where the transvers voltage drop (Nernst voltage) driven by temperature
gradient is proportional to magnetization. However, most recent progress shows thateven higher anomalous Nernst voltage can be generated in non-ferromagneic material
Mn3Sn[1], 0.35µV/K and 0.6µV/K, at 300K and 200K, respectively, with a very tinymagnetization, which has been confirmed to come from the Weyl nodes providing large
Berry curvature near the Fermi level[2,3].
Compared to Mn3Sn, Mn3Ge has the same crystal structure and inverse spin
structure [4], but possibly may provide much more Weyl nodes close to the Fermi level
because of the smaller spin orbit coupling for Germanium in comparison with Tin[5],and thus might lead to higher anomalous Nernst effect and anomalous Hall effect. For
the anomalous Nernst effect in Mn3Ge, works have not been reported. Here, highquality of Mn3Ge single crystals are synthesized both by flux and Bridgman method.
Our thermoelectric measurements show that the highest anomalous Nernst effect canreache up to 0.45µV/K and 1.3µV/K at room temperature and 100K, respectively, twice
higher than the value reported for the antiferromagnet Mn3Sn. In addition, the obvious
negative magneto-resistivity is observed when external magnetic field is applied parallelto the electric current both in and out of Kagome plane configurations, consistent withthe existence of Weyl nodes close to the Fermi energy. This makes it an ideal platform
for deep understanding of the intrinsic anomalous Hall effect and a good candidate forthe high thermoelectric harvesting efficiency device design.
[1] S. Nakatsuji, N. Kiyohara and T. Higo Nature 527, 212 (2015)[2] M. Ikhlas, T. Tomita et. al., Nature Physics 13, 1085 (2017).
[3] K. Kuroda and T. Tomita et al. Nat. Mater. 16,1090 (2017)[4] N. Kiyohara, T. Tomita and S. Nakatsuji Phys. Rev. Appl. 5, 064009 (2016)[5] Z. Yang et al. Phys. Rev. B. 95.075128 (2017)

77

P35
Non-hermitian properties in non-centrosymmetricf-electron materials
Y. Michishita1and R. Peters1
1Institute for Science Physics, Kyoto University, Japan
Recently, the physics described by effective non-hermitian Hamiltonian are intensively
studied especially in the context of open quantum systems.[1,2] Effective non-hermitian
Hamiltonian can be allowed in open quantum systems while the isolated system should be
described by hermitian Hamiltonian in the scheme of quantum mechanics.
On the other hand, in strongly correlated systems(SCS), particles have the self-energy
which contains finite imaginary part and therefore SCS can be also described by the effective
non-hermitian Hamiltonian. Conventionally, the effect of imaginary part of the self-energy wasconsidered just broadening the density of states of the bands. However, last year, Liang Fu’s
group proposed that this effective non-hermiticity sometimes gives drastic effect.[3] It gives
the exceptional points(EPs) where the effective non-hermitian Hamiltonian cannot be
diagonalized and the topological number can be defined. Moreover, when there are EPs at the
Fermi surface, the bulk Fermi arc emerges between EPs. These non-hermitian effect in SCS
has the potential to explain the pseudo-gap in cuprate superconductors and the quantum
oscillation in topological Kondo insulator.[4]In this poster, we show the non-hermitian effect of the self-energy in 2D and 3D noncentrosymmetric f-electron materials by numerical calculation with DMFT/NRG. We use theperiodic Anderson model which is one of the minimum model that satisfies the condition for
the emergence of the bulk Fermi arc. We proposed that non-centrosymmetric f-electronmaterials can be one of the good platform for studying non-hermitian effect in SCS. For noncentrosymmetric cases, one of the Kondo gap becomes small due to the spin splitting.[5] Our
results shows that when we add the enough anti-symmetric spin-orbit coupling(Rashba SOC in
this work) ,for examples by the substitution, the Kondo gaps becomes smaller than theimaginary part of the self-energy and the bulk Fermi arc emerges. Moreover, if we add more
RSOC, it splits.[6][1] A. Author, B. Second and C. Third, PRX 8, 031079 (2018).
[2] L. Feng, R. El-Ganainy and L. Ge, http://doi.org/10.1038/s41566-017-0031-1(2018)[3] H. Shen, B. Zhen and L. Fu, PRL 120, 146402(2018)[4] G. Li , et al, Science 346, 1208-1212 (2014)[5] Suchitra E. Sebastian, et al, Science 349,287-290 (2015)[6] YM and R. Peters “Impact of Rashba Spin Orbit Coupling on f-electron materials ” soon
[7] YM and R. Peters “Non-hermitian propeties in non-centrosymmetric f-electron materials”
coming soon.

78

P36
Atomic-scale structural and electronic properties
of YbB12(001) surfaces
T. Miyamachi1, K. Iwata1, T. Iimori1, Y. Ohtsubo2, S. Kimura2, F. Iga3, and F. Komori1
1
Institute for Solid State Physics, The University of Tokyo, Japan2
Department of Physics, Graduate School of Science, Osaka University, Japan
3
College of Science, Ibaraki University, Japan
A Kondo insulator YbB12 revives its interest owing to the recent theoretical prediction as apossible candidate for a topological Kondo insulator [1]. The experimental identification of
topological surface states, which can explain the resistance plateau of YbB12 at low
temperatures, is necessary toward understanding of intrinsic electronic properties of strongly
correlated topological insulators.
In this work, we use scanning tunneling microscopy (STM) to investigate structural andelectronic properties of the YbB12(001) surface on the atomic scale. The flat surface of the
YbB12(001) single crystal was prepared by annealing [2] instead of the conventional cleavage.
We demonstrate that the quality of the YbB12(001) surface strongly depends on the annealing
procedures. Furthermore, atomically-resolved spatial dependences of the differential
conductance spectrum near the Fermi energy reveal that the in-gap state emerging inside the
Kondo hybridization 4.4 K is a robust surface state against structural variations.
[1] H. Weng et al., Phys. Rev. Lett. 112, 016403 (2014).
[2] K. Hagiwara et al., Nat. Commun. 7, 12690 (2016).

79

P37
Majorana edge magnetization in the Kitaev honeycomb
model
T. Mizoguchi1 and T. Koma2
1
Department of Physics, University of Tsukuba, Japan2
Department of Physics, Gakushuin University, Japan
Detecting Majorana fermions has attracted great interests recently in condensed matterphysics. One of the promising candidates is the Kitaev honeycomb magnet [1], which is anexactly solvable quantum spin model with Majorana-type excitations. The exact solvability
comes from the fact that the model can be mapped to a free Majorana fermion model by using
the Jordan-Wigner transformation [2]. Besides, the free Majorana fermion model thus obtained
has a weak topological character, namely, it belongs to BDI class in two dimensions. This
weak topological character is reflected to the Majorana flat bands at the edges [3]. However, it
has not been clarfied how to observe the Majorana edge flat bands in experiments.
In this presentation, we propose an approach to detect the Majorana fermions at the edges bymeasuring the edge magnetization. By using a standard technique to diagonalize free fermion
models, we show that there appears a unidirectional magnetization without any transverse
magnetization when applying a sufficiently weak magnetic field [4]. This peculiar behavior of
the edge magnetization is expected to be a clue to detect Majorana fermions in experiments.

1.0

0.8

0.6

0.4

z
x

y

Figure 1: The Kitaev’s honeycomb model (left) and the edge
magnetization in Ay phase (right).
[1] A. Kitaev, Ann. Phys. 321, 2 (2006).
[2] X.-Y. Feng, G.-M. Zhang, and T. Xiang, Phys. Rev. Lett. 98, 087204 (2007).
[3] M. Thakurathi, K. Sengupta, and D. Sen, Phys. Rev. B 89, 235434 (2014).
[4] T. Mizoguchi and T. Koma, arXiv:1811.10895.

80

P38
Large anomalous Hall effect in topological insulatorswith proximitized ferromagnetic insulators
M. Mogi1, T. Nakajima2, V. Ukleev2,3, A. Tsukazaki4, R. Yoshimi2, M. Kawamura2, K.
S. Takahashi2, T. Hanashima6, K. Kakurai2,5, T. Arima2,6, M. Kawasaki1,2 and Y.
Tokura1,2
1
Department of Applied Physics, The University of Tokyo, Japan
2
RIKEN Center for Emergent Matter Science (CEMS), Japan
3
Laboratory for Neutron Scattering and Imaging (LNS), Paul Scherrer Institute (PSI),
Switzerland
4
Institute for Materials Research, Tohoku University, Japan
5
Comprehensive Research Organization for Science and Society (CROSS), Japan
6
Department of Advanced Materials Science, The University of Tokyo, Japan
In magnetically-doped topological insulator thin films, exotic magnetic quantum phasessuch as the quantum anomalous Hall insulator and axion insulator have been achieved [1,2].
The formation of a mass gap at the Dirac surface state on the topological insulators and the
Fermi-level tuning into the gap are both requisite to the emergence of such topological states,
being realized not only by magnetic doping but also by proximitizing ferromagnetic insulators.
However, the magnitude of electronic responses or the proximity-coupling strength to thesurface states remains far smaller than expected.
Here, we report a proximity-driven large anomalous
Hall effect in all-telluride heterostructures consisting of aferromagnetic insulator Cr2Ge2Te6 and a topologicalinsulator (Bi,Sb)2Te3. The anomalous Hall conductanceemerges in accord with a ferromagnetic response of the
Cr2Ge2Te6 layer, while no discernible magnetization isdetected in the (Bi,Sb)2Te3 layer by spin-polarized
neutron reflectometry. The results show that theexchange coupling between the surface state of the Figure 1: Schematic drawing of
coupling
between
topological insulator and the proximitized Cr2Ge2Te6 proximity
insulators
andlayer is effective enough to open the sizeable mass gap topologicalferromagnetic insulatorsin the surface state.
[1] C.-Z. Chang et al., Science 340, 167 (2013).
[2] M. Mogi, M. Kawamura, R. Yoshimi, A. Tsukazaki, Y. Kozuka, N. Shirakawa, K. S.
Takahashi, M. Kawasaki and Y. Tokura, Nat. Mater. 16, 516 (2017).

81

P39
Topologically Enhanced Anomalous Nernst Effectin Half-Heusler Ferromagnet CoMnSb
H. Nakamura1, P.A. Yan2, T. Tomita1, 7, A. A. Nugroho2, S. Minami3,
F. Ishii4, M. Saito5, T. Koretsune6, and S. Nakatsuji1, 7
1
Institute for Solid State Physics, The University of Tokyo, Japan
2
Institut Teknologi Bandung, Indonesia
3

Graduate School of Natural Science & Technology, Kanazawa Univ., Japan
4
NanoMaRI, Kanazawa Univ., Japan
5
School of Mathematics and Physics, Kanazawa Univ., Japan
6
Graduate School of Science and Faculty of Science, Tohoku Univ., Japan
7

CREST, Japan Science and Technology Agency, Japan

Recently a large anomalous Nernst signal comparable in size to ordinal ferromagnets wasfound to appear in antiferromagnet Mn3Sn, showing tiny magnetization [1]. The size ofanomalous Nernst effect (ANE) has ever been believed to be proportional to magnetization.
This unexpected large ANE was explained by the large fictitious magnetic field in
momentum-space (Berry curvature) induced by magnetic Weyl points. A ferromagnetic Weyl
material, moreover, is theoretically proposed and experimentally verified in full-Heusler
compound Co2MnGa, where a remarkably high ANE value of 6 μV/K was observed at room
temperature [2] as well.
Very recently, large size of Berry curvature was proposed by the first-principle calculation in
half-Heusler ferromagnet CoMnSb[3], exhibiting the Nernst coefficient as high as 1.2 μV/K at
300 K. To confirm its Nernst signal size experimentally, we synthesized a single-crystal sample
and measured its thermoelectric properties. As a result, we observed a Nernst signal of 0.5 μV/K
at 300 K. This size is smaller than the calculated result but expected to be further enhanced bytuning Fermi energy EF. In addition, transverse thermoelectric conductivity αxy (T) obtained
from our experimental results behaved as -T log T at high temperature as well as observed in
Co2MnGa[2]. This characteristic behavior suggests that the Weyl point exist in the vicinity of EF
in CoMnSb.
[1] M. Ikhlas, T. Tomita et al., Nature Physics 13, 1085 (2017).
[2] A. Sakai et al., Nature Physics 14, 1119 (2018).
[3] S. Minami et al., Applied Physics Letters 113, 032403 (2018).

82

P40
In-plane field and current dependence of
the Josephson effect in Nb/InAs/Nb junctions
T. Nakamura1, Y. Hashimoto1 and S. Katsumoto1,2
1
Institute for Solid State Physics, The University of Tokyo, Japan
2
Center for Spintronics Research Network, The University of Tokyo, Japan
Spin-orbit coupling (SOC) is an important ingredient of interesting phenomena such as thespin Hall effect [1] and topological superconductivity [2], in combination with time-reversal
symmetry (TRS) breaking perturbation. In-plane magnetic fields applied to 1D or 2D
superconducting junctions enable us to access such novel systems because they lift the spin
degeneracy with little orbital effects [3]. In this work, we fabricated superconducting junctions
with a two-dimensional electron systems (2DESs) in InAs quantum wells, suitable forinvestigation of superconducting phenomena since they provide good electric contact to thesuperconductors and Rashba-type strong spin-orbit coupling (SOC) is expected in 2DESs at
spatially asymmetric structures of quantum wells.
Two Nb electrodes are attached to a 2DES as shown in Fig. 1 and external magnetic fields
were applied along in-plane and out-of-plane directions independently. The junctions exhibit
zero-resistance and their critical current Ic oscillates against the out-of-plane field. Without inplane magnetic fields, this pattern is a well-known Fraunhofer-like pattern, which has a peak at
the zero field. However, under in-plane fields, the pattern becomes asymmetric and the
maximum Ic decreases. This is attributable to vortex pinning and field modulation due to
Meissner effect of the electrodes [3]. In contrast to the in-plane fields, the mesa current reduces
the Ic monotonically as shown in Fig. 2. This reduction cannot be explained by either heatingor potential shift in the mesa. We are
discussing other mechanisms of Ic
reduction, for example, spin Hall effect orZitterbewegung.

Fig. 2: Differential resistance as a function ofFig. 1: SEM image of a sample.

Junction current and mesa current.

[1] J. Sinova, et al., Rev. Mod. Phys. 87, 1213 (2015).
[2] Steven R. Elliott and Marcel Franz, Rev. Mod. Phys. 87, 137 (2015).
[3] S. Hart et al., Nat. Phys. 13, 87 (2017), and H. J. Suominen et al., Phys. Rev. B 95, 035307(2017).

83

P41
Non-equilibrium dynamics by field quench in Kitaev model
Joji Nasu1 and Yukitoshi Motome2
1 Department of Physics, Yokohama National University, Japan
2 Department of Applied Physics, University of Tokyo, Japan

Insulating magnets provide a good playground for quantum many-body eﬀects on the spin
degree of freedom of electrons in solids. While the spins are usually frozen with magnetic
ordering at the lowest temperature, P. W. Anderson suggested that they could remain melting due
to strong quantum fluctuations [1], which leads to a new state of matter, the quantum spin liquid(QSL). This state has attracted great interest for a number of decades as it could exhibit topologicalorder and possess fractional excitations with unconventional statistics. Particularly, the Kitaev
model has been intensively investigated as its ground state is exactly shown to be a QSL withMajorana excitations fractionalized from quantum spins [2]. Although a lot of attempts have been
devoted to the observations of the fractional quasiparticles, the experimental identification remains
elusive. This is because the fractional quasiparticles hardly couple with experimental probes.
In this study, to observe the fractional excitations separately, we focus on time evolution of
their non-equilibrium dynamics. In our previous work, we examined the magnetic-field eﬀect
on the ferro- and antiferro-magnetic Kitaev models using the Hartree-Fock approximation in the
Majorana fermion representation [3]. Here, we study the transient magnetic dynamics yielded by
the magnetic-field quench by extending the previous work. In the Kitaev model, a quantum spinis fractionalized into low-energy localized Majorana fermions and high-energy itinerant ones. We
find that two kinds of Majorana fermions are observed separately in distinct time-scales in thetime evolution of the magnetization. On the other hand, this behavior disappears in the forced
ferromagnetic phase realized in the high-field case.

[1] P. W. Anderson, Mater. Res. Bull. 8, 153 (1973).
[2] A. Kitaev, Ann. Phys. (N. Y.) 321, 2 (2006).
[3] J. Nasu, Y. Kato, Y. Kamiya, and Y. Motome, Phys. Rev. B 98, 060416(R) (2018).

84

P42
Quasi-1D bismuth halides exhibiting various topologicalphases investigated by ARPES
R. Noguchi1, T. Takahashi2, K. Kuroda1, C. Bareille1, S. Sakuragi1, S. Kunisada1,
K. Kurokawa1, T. Kim3, C. Cacho3, S. Shin1, T. Sasagawa2, T. Kondo1
1
ISSP, Univ. of Tokyo, 2MSL, Tokyo Tech., 3Diamond Light Source
Topological insulators are a class of materials with metallic surface/edge states due to nontrivial electronic structures in the bulk [1]. After theoretical predictions, various materials havebeen confirmed to show topologically non-trivial properties through the observing
surface/edge states [2,3]. Recently, quasi-one-dimensional (quasi-1D) bismuth halides Bi4X4(X=Br, I) [4] are theoretically predicted to be in the proximity of topological phase transitions[5-7]. However, the determination of their topological phases is difficult only by theoretical
calculations, since their band gap sizes and the numbers of band inversions are very sensitive
to the computational parameters. Therefore, the direct observation of the band structures by
ARPES is necessary to reveal their topological properties. So far, we have experimentallyshown that β-Bi4I4 is a weak topological insulator with quasi-1D surface states on its sidesurface, and α-Bi4I4 is a trivial insulator due to its bilayer structure [8]. In contrast,
experimental study on Bi4Br4 has been lacked, despite the prediction that it is a topologicalcrystalline insulator with helical hinge states protected by a C2 rotation symmetry [7].
In this contribution, we will present our(a)(b)(001) surface BZ
latest ARPES results of Bi4Br4. The measuredkkFermi surface consists of island-like featuresΓBi bulk BZ
at the M point of the (001) surface Brillouin
c*
Z
Br
b*
J
zone similarly to the case of α-Bi4I4. The band
L
K
Γ
a*
Y
dispersion along kx axis is faster than α-Bi4I4,
M
Z
X
reflecting the smaller distance between Bi
atoms along a-axis. More details of theelectronic structure of Bi4Br4 will be Figure 1: (a) Crystal structure and (b) the bulk
discussed in the poster.
and surface projected Brillouin zone of Bi4Br4.
x[1] L. Fu and C. L. Kane, Phys. Rev. B 76, 45302 (2007).
[2] Y. Xia et al., Nat. Phys. 5, 398 (2009).
[3] Y. L. Chen et al., Science 325, 178 (2009).
[4] H.G. von Schnering et al., Z. Anorg. Allg. Chem. 438, 37–52 (1978).
[5] G. Autès et al., Nat. Mater. 15, 154 (2015).
[6] C.-C. Liu et al., Phys. Rev. Lett. 116, 66801 (2016).
[7] F. Tang, H. C. Po, A. Vishwanath, and X. Wan, arXiv 1805.07314 (2018).
[8] R. Noguchi et al., Nature, accepted (2018).

85

y

P43
Spontaneous Hall effectin a Luttinger semimetal Pr2Ir2O7 thin film
T. Ohtsuki1, Z. Tian1, A. Endo1, M. Halim1, S. Katsumoto1, Y. Kohama1, K. Kindo1,
M. Lippmaa1, and S. Nakatsuji1,21
Institute for Solid State Physics, The University of Tokyo, Japan
2
CREST, Japan Science and Technology Agency (JST), Japan
In 5d electron systems represented by iridates, spin-orbit and Coulomb interactions areof approximately the same order of magnitude. It has been theoretically predicted that as aresult, novel topological phases such as Weyl semimetal and strongly correlated topologicalinsulator states may emerge [1]. We have focused on a pyrochlore iridate, Pr 2Ir2O7, and foundseveral interesting physical properties [2-5]: it is metallic down to the lowest temperatures but
behaves as a spin liquid [2, 3]; it exhibits spontaneous Hall effect generated by spin chirality[4]; and it has a Fermi node formed by quadratic band touching of the doubly degeneratevalence and conduction bands at the Г point at the Fermi level [5]. Moreover, we successfully
fabricated (111)-oriented pyrochlore Pr2Ir2O7 epitaxial thin films [6, 7]. The spontaneous Hall
effect in the thin films appears up to about 50 K which is higher than the bulk report, and it islikely that the Weyl semimetal phase exists in the Pr2Ir2O7 thin films.

When we measure the magnetic field dependence of magnetoresistance (MR) at
2 K in the configurations where the magnetic field (B) is either perpendicular (B⊥I,
B//[110]) or parallel (B//I, B//[11̄0]) to the current, which experimental configurations
are crystallographically equivalent, both MR curves show negative MR due to the 2-in2-out spin configuration. In contrast, the negative MR is larger when the magnetic field
is parallel to the current. In the presentation, we will analyze the difference in the MR
curves, and discuss the origin of the effect, such as a chiral magnetic effect.
[1] W. Witczak-Krempa et al., Annu. Rev. Condens. Matter Phys. 5, 57 (2013).
[2] S. Nakatsuji et al., Phys. Rev. Lett. 96, 087204 (2006).
[3] Y. Tokiwa et al., Nat. Mater. 13, 356 (2014).
[4] Y. Machida et al., Nature 463, 210 (2010).
[5] T. Kondo et al., Nat. Commun. 6, 10042 (2015).
[6] T. Ohtsuki et al., arXiv:1711.07813 (2017).
[7] B. Cheng, T. Ohtsuki et al., Nat. Commun. 8, 2097 (2017).

86

P44
Numerical study of nonreciprocal spin current inmonoaxial chiral magnets
S. Okumura1, H. Ishizuka1, Y. Kato1, J. Ohe2, and Y. Motome1
1
Department of Applied Physics, The University of Tokyo, Japan2
Department of Physics, Toho University, Japan
Chiral magnets often show interesting properties associated with their peculiar spin structures
originating from the antisymmetric exchange interaction called the Dzyaloshinkii-Moriya
interaction. A typical example is found in a monoaxial chiral magnet CrNb3S6 [1]. While thiscompound shows a chiral helimagnetic state at zero magnetic field, it turns into a chiral conicalmagnetic state in a field parallel to the helical axis (Figure 1). The chiral magnetic structurespotentially give rise to nonreciprocal transport phenomena, as they break spatial inversion andtime reversal symmetries simultaneously [2]. However, such interesting possibilities have notbeen fully explored, especially for charge and spin currents.
In the present study, we investigate the spin-dependent transport in the chiral conical magnetic
states using a minimal itinerant electron model, a one-dimensional Kondo lattice model. The
conductance of spin current is calculated numerically by using a Landauer-type formula based on
a Green’s function method. We show that the system exhibits nonreciprocal spin transport, which
depends on the angle of conical spins, the chirality of the magnetic structures, and the polarized
direction of the spin current (Figure 2). We discuss the origin of the nonreciprocity by analyzing
the spin states near the edges [3].
Right-handed

Left-handed

Figure 1: Schematic pictures of (a) a chiralhelimagnetic state and (b) a chiral conicalmagnetic state.

Figure 2: The conical angle φ and chirality
dependence of the difference of thetransmittances ∆𝑡 𝑧 between right- and leftgoing spin current polarized along the 𝑧 axis.

[1] T. Miyadai et al., J. Phys. Soc. Jpn. 52, 1394 (1983).
[2] G. Rikken et al., Phys. Rev. Lett. 87, 236602 (2001).
[3] S. Okumura, H. Ishizuka, Y. Kato, J. Ohe, and Y. Motome, in preparation.

87

P45
Magnetic phase diagram of an orthorhombic Kagomé
cobaltite CaBaCo4O7
Tsuyoshi Omi1 , Nobuyuki Abe1 , Yusuke Tokunaga1 and Taka-hisa Arima1
1 Department of Advanced Materials Science, The University of Tokyo, 277-8561

Kashiwa, Japan
Magnetic frustration often plays an important role in multiferroic properties as is exemplified
by the electric polarization induced by the spiral magnetic order. CaBaCo4 O7 is a multiferroic
material hosting magnetic frustration[1] exhibiting the largest electric polarization change about 17
mC/m2 at the ferrimagnetic transition so far among all the multiferroic materials[2]. CaBaCo4 O7
belongs to the space group Pbn21 . Magnetic Co ions form Kagomé- and trianglar- lattice layers,which alternately stack along the c-axis.
CaBaCo4 O7 shows a ferrimagnetic transition at Tc ∼ 60 K at zero magnetic field. The
specific heat and the electric permittivity of single crystal CaBaCo4 O7 exhibits another anomaly at
T ∗ ∼ 69 K slightly higher than Tc in zero mangetic field, while the origin of the anomaly was notclarified[2]. We have measured the magnetization and elastic constants in detail, our present result
reveals that paramagnetic-antiferromagnetic transition occurs at T ∗ . Furthermore, we propose amagnetic phase diagram of CaBaCo4 O7 (Fig. 1) in the B-T plane based on the measurement ofelastic constants C11, C55, C66 . The transition magnetic field was determined by a measurement of
the magnetization of detwinned sample.

[1] Zhe Qu, Langsheng Ling, Lei Zhang, Li Pi,
Yuheng Zhang, Solid State Commun. 151, 917919 (2011).

C11

Ferrimagnetic

C55
C66

PM

[2] V. Caignaert, A. Maignan, K. Singh, Ch. Simon, V. Pralong, B. Raveau, J. F. Mitchell, H.
Zheng, A. Huq, and L. C. Chapon, Phys. Rev.
B 88, 174403 (2013).

Tc

AFM
T*

Figure 1: Magnetic phase diagram of CaBaCo4 O7 forthe magnetic field parallel to the b axis.

88

P46
Supercurrent on accumulation edges of an InAs quantum
well
M. Onizaki, Y. Hashimoto, T. Nakamura and S. Katsumoto
Institute for Solid State Physics, The University of Tokyo, Japan
Though a superconductor has an energy gap opening at the Fermi level, the Andreev
reflection mechanism (ARM) connects metallic states and condensate of Cooper pairs
adiabatically [1] at the metal-superconductor interface. Here strong interest exists in the case
we replace the metal with an insulator with non-trivial topology like a quantum Hall insulator(QHI). Some theories predict the conductive states at the quantum Hall edge are connected tothe condensate adiabatically via the ARM. In such a situation a single edge state works both as
an electron and a hole conduction channel, hence bears double of the quantum conductance
2Gq (Gq=2e2/h). Connecting one edge to a normal electrode disturbs creation of hole edge
channels, enabling study of the other edge exclusively.
We fabricated NbTi/2-dimensional electron gas (2DEG)/NbTi junctions from an InAs
quantum well with inverted modulation doping (The mobility and the concentration are
1.66×104 cm2/Vs and 2.11×1012cm-2, respectively). On one edge, a trench-type quantum point
contact was fabricated (Fig. (a)). With increasing the negative gate voltage, the critical current
was strongly reduced (Fig. (b)), while the period of the interference pattern was kept constant(Fig. (c) and (d)). The latter result means that the gate voltage gives little change in the area forthe supercurrent to flow. We hence infer that edge channels are formed by charge
accumulation and they sustain large amount of supercurrent, which are depleted by applying
negative gate voltage.
(a)

(c)

(b)

(d)

[1] P. W. Anderson, Basic
Notions of Condensed Matter
Physics (Benjamin, 1984).

Figure: (a) Optical micrograph of the sample. (b) Color plot of dV/dI. (c) Magnetic interferance
pattern dV/dI with gate voltage 0 V and (d) -12 V, respectively.

89

P47
Symmetry Indicators for Topological Superconductors
S. Ono1, Y. Yanase2 and H. Watanabe3
1Institute for Solid State Physics, The University of Tokyo, Japan2
Department of Physics, Kyoto University, Japan2
Department of Applied Physics, The University of Tokyo, Japan
Many people are making efforts to investigate the relationships between topology andsymmetry, especially searching for topological crystalline insulators (TCI) and topologicalsuperconductors (TSC). L. Fu and C. L. Kane proposed the first efficient way to discover TI,
called Fu-Kane formula [1], which is applicable to inversion symmetric systems. Recently,
there have been fundamental advances in the method of symmetry indicators [2] and in asimilar formalism, which provide an efficient way to diagnose the topology of band insulatorsand semimetals based on the representations of valence bands at high-symmetry momenta.
This scheme can be understood as a generalization of the Fu-Kane formula that computes the
topological index in terms of inversion parities to arbitrary space groups and a wider class of
topologies including higher-order ones. It formed the basis of recent extensive material
searches based on the density functional theory (DFT) calculation by several groups that
resulted in the discovery of an enormous number of new topological materials [3-5]. Up to thismoment, however, symmetry indicators are applicable only to insulators and semimetals inwhich a fixed number of valence bands exist below the Fermi level at every high-symmetry
momentum. If one wants to apply this method to SCs, one must examine the representations in
the band structure of the Bogoliubov-de Gennes (BdG) Hamiltonian including a gap function.
In fact, this is the approach taken in Ref. [6] that recently extended the symmetry indicators to
the 10 Altland-Zirnbauer symmetry classes. However, this is not ideal because such a band
structure is not available in the standard DFT calculation. Furthermore, in this way, the total
number of bands that have to be taken into account can be huge unless one uses an effective
tight-binding model.
In this work, we further develop the theory of symmetry indicators exclusively designed forSCs. It enables us to determine the topology of SCs based on the representations of a finite
number of bands below the Fermi surface in the normal phase, although one still has to assume
a symmetry transformation property of the gap function [7].
[1] L. Fu and C. L. Kane, Phys. Rev. B, 76, 045302 (2007).
[2] H. C. Po, A. Vishwanath, and H. Watanabe, Nat. Commun 8, 50 (2017).
[3] T. Zhang, Y. Jiang, et al., arXiv:1807.08756.
[4] F. Tang, H. C. Po, et al., arXiv:1807.09744.
[5] M. G. Vergniory, L. Elcoro, et al., arXiv:1807.10271.
[6] S. Ono and H. Watanabe, Phys. Rev. B. 98, 115150 (2018)[7] S. Ono, Y. Yanase, and H. Watanabe, arXiv:1811.08712.

90

P48
Quantum oscillations in topological Kondo insulator
R. Peters1, T. Yoshida2 and N. Kawakami1
1
Kyoto University, Kyoto, Japan
2
University of Tsukuba, Tsukuba, JapanOne of the most puzzling recent experimental discoveries in condensed matter physics has
been the observation of quantum oscillations in insulating materials SmB6 and YbB12 [1,2].
Our understanding of quantum oscillations is rooted in the existence of a Fermi surface;electron bands, which form the Fermi surface, form Landau levels in a magnetic field. Whenthe magnetic field strength is changed, the energy of these Landau levels changes which leadto an oscillatory behavior in almost all of the observable properties. However, SmB6 andYbB12 are strongly correlated f electron systems for which a gap develops due to a
hybridization between conduction electrons and strongly correlated f electrons, and thus a large
resistivity at low temperatures can be measured. Thus, we can expect that SmB6 and YbB12
do not possess a Fermi surface, thus there are no electrons, which can form Landau levels,
close to the Fermi energy. On the other hand, SmB6 and YbB12 are both good candidates for
topological Kondo insulator. Naturally, the question arises, if these quantum oscillations canbe due to the interplay between non-trivial topology and strong correlations.
We here answer this question by showing results of dynamical mean field theory in amagnetic field for a two dimensional topological Kondo insulator. We demonstrate that the gap
closing, described for a noninteracting continuum model with momentum dependent
hybridization [3], persists for a topological Kondo insulator on a two dimensional (2D) lattice.
Furthermore, we demonstrate that the amplitude of quantum oscillations is strongly enhanced
due to correlations, which makes them easily observable in quantities like magnetization andresistivity over a wide range of magnetic fields before the magnetic breakdown occurs.
[1] Tan et al. Science 349, 287 (2015)[2] Z. Xiang et al. in Science (2018)[3] Long Zhang et al. Phys. Rev. Lett. 116, 046404 (2016)

91

P49
Spin to charge conversion via magnon-phonon coupling
J. Puebla1, M. Xu2, F. Auvray2, B. Rana1, K. Kondou1, Y. Otani1,21Center of Emergent Matter Science, RIKEN
2
Institute for Solid State Physics, The University of Tokyo, JapanWe demonstrate a spin to charge current conversion via magnon-phonon coupling and an
inverse Edelstein effect on the hybrid device Ni/Cu(Ag)/Bi2O3. The generation of spin current(Js ≈ 108 A/m2) due to magnon-phonon coupling reveals the viability of acoustic spin pumping
as a mechanism for the development of spintronic devices. A full in-plane magnetic field angle
dependence of the power absorption and a combination of longitudinal and transverse voltage
detection reveals the symmetric and asymmetric components of the inverse Edelstein effectvoltage induced by Rayleigh-type surface acoustic waves. While the symmetric components
are well studied, asymmetric components still need to be explored. We assign the asymmetriccontributions to the interference between longitudinal and shear waves and an anisotropic
charge distribution in our hybrid device.

(a)

(b)

Figure 1. Schematic representation of acoustic spin pumping device in our study (a), andschematic of spin to charge conversion mechanism induced by magnon – phonon coupling (b).

[1] M. Xu, J. Puebla, F. Auvray, B. Rana, K. Kondou, Y. Otani, Physical Review B 97(18), 180301 (2018)
Research highlights RIKEN

92

P50
Spin-dependent diode performance in fully epitaxial
magnetic tunnel junctions with rock-salt type ZnO/MgO
bilayer tunnel barrier
H. Saito1, S. Kon1,2, N. Sai Krishna3, N. Matsuo1,2, N. Doko1,2, Y. Yasukawa2,
H. Imamura1, and S. Yuasa1
1
AIST, Spintronics Research Center
2
Chiba Institute of Technology
3
NIMS, Research Center for Magnetic and Spintronic Materials
Metal/insulator/metal (MIM) and metal/insulator/insulator/metal (MIIM) tunnel diodes havegreat potential for high-frequency rectifier systems, such as for THz/infrared detectors andradio-frequency energy harvesting applications [1,2]. Amorphous or polycrystalline tunnel
barriers have often been used in both MIM and MIIM diodes, and a single-crystalline tunnel
barrier has never been used despite its high potential for tunnel-device applications. Here, wereport on the spin-dependent diode properties of fully epitaxial Fe/ZnO/MgO/Fe(001)magnetic tunnel junctions (MTJs) with a MIIM structure, in which ZnO has a metastable rocksalt crystal structure. Note that, for these MTJs, the operation principle of the rectifying
process does not come from a spin-torque diode effect [3] but from intrinsic nonlinear and/or
asymmetric current-voltage (I-V) characteristics.
MTJ films were prepared by molecular beam epitaxy. The structure of the MTJ was Au (5nm) / Co (10 nm) / Fe (5 nm) / ZnO (1.2 nm) / MgO (1 nm) / Fe (30 nm) /MgO(001) substrates.
Crystallographic studies, such as RHEED and TEM observations, revealed that the ZnO tunnel
barriers are single-crystalline with a rock-salt crystal structure. Magnetoresistance ratios up to
96% (127%) were observed at RT (20 K).
We found that the MTJs exhibited notable asymmetric I-V characteristics due to the bilayer
tunnel barrier, and those diode properties strongly depended on the magnetization alignment of
the Fe electrodes. The current responsibilities of the MTJs were largely enhanced at the antiparallel alignment (2 ~ 3 A/W at RT) and almost comparable to those of high-performance
MIIM diodes with dissimilar electrodes [4] as well as to a state-of-the-art spin-torque diode[2,5]. We demonstrated that a zero-bias anomaly in the tunnel conductance, which originatesfrom the magnon excitations at the Fe/barrier interfaces, plays a crucial role in observed spindependent diode performance.
This work was supported by the Grant-in-Aid for Scientific Research on Innovative Area,“Nano Spin Conversion Science” (Grant °No. 26103003).
[1] S. Grover, and G. Moddel, Solid State Electron. 67, 94 (2012).
[2] S. Hemour and K. Wu, Proc. IEEE. 102, 1667 (2014).
[3] A. A. Tulapurkar, et al, Nature 438, 339 (2005).
[4] S. B. Herner, et al, Appl. Phys. Lett. 110, 223901 (2017).
[5] S. Miwa, et al. Nat. Mater. 13, 50 (2014).

93

P51
Giant anomalous Nernst effect at room temperaturein Co2MnGa
A. Sakai1, Y. P. Mizuta3,4, A. A. Nugroho1,5, R. Sihombing1,5,
T. Koretsune2,4, M.-T. Suzuki2,4, N. Takemori4, R. Ishii1, D. N.-Hamane1, R. Arita2,4,
P. Goswami6,7 &, S. Nakatsuji1,21

Institute for Solid State Physics, The University of Tokyo, Japan
2
CREST, Japan Science and Technology Agency (JST), Japan
3
Faculty of Mathematics and Physics, Kanazawa University, Japan
4
Center for Emergent Matter Science, RIKEN, Japan
5
Faculty of Mathematics and Natural Sciences, Bandung Institute of Technology,
Indonesia,
6
Condensed Matter Theory Center and Joint Quantum Institute, Department of
Physics, University of Maryland, USA
7
Department of Physics and Astronomy, Northwestern University, USA

Thermoelectric generation based on the Seebeck effect have been studied intensively to
overcome the energy problem. On the other hand, metallic ferromagnets show the electric
voltage perpendicular to both magnetization and an applied temperature gradient, so called theanomalous Nernst effect (ANE). This transverse geometry enables a lateral conﬁguration of thethermoelectric modules to efﬁciently cover a heat source compared to the conventional Peltier
device [1]. However, the size of ANE is too small for practical applications.
Recent theoretical and experimental investigations on topological material have indicatedthat the intense Berry curvature of Weyl points near the Fermi energy can potentially enhance
the intrinsic ANE [2-4]. Thus, there must be some materials which can show large ANE insuch Weyl magnets.
Here, we report the giant ANE in the full-Heusler ferromagnet Co2MnGa, reaching arecord high value Syx ~6 V/K at room temperature [5]. The crossover from Mott relation ayx ~T to −lnT dependence is observed on warming, indicating the proximity to the quantum
Lifshitz transition between type-I and type-II magnetic Weyl fermions.

[1] Y. Sakuraba et al., Appl. Phys. Express 6, 033003 (2013).
[2] D. Xiao et al., Rev. Mod. Phys. 82, 1959–2007 (2010).
[3] M. Ikhlas et al., Nat. Physics 13, 1085 (2017).
[4] K. Kuroda et al., Nat. Mater. 16, 1090 (2017).
[5] A. Sakai et al., Nat. Physics 14, 1110 (2018).

94

P52
Chirality inversion and thermal Hall eﬀect in Weyl
superconducting state of URu2Si2
Naoki Sakamoto1 , Youichi Yanase1
1 Condensed Matter Theory Group, Department of Physics, Graduate School of Science,

Kyoto University
In URu2 Si2 , U atoms form body centred tetragonal structure with anisotropy in the c-axis direction and have sublattice degree of freedom. Below approximately 0.75GPa and 1.4K, it is found thatchiral d-wave superconductivity is realized. Moreover, below approximately 17.5K, so-called hidden ordered phase is realized. The Fermi surface exists around the M points in k space, and there arepoint nodes at the north and south poles of the Fermi surface and horizontal line node at the surfaceof k z = 0 [1, 2]. These point nodes are weyl nodes, which are protected by topological number [3, 4].
The Chern numbers, which are defined on 2D surface, of Weyl superconductors when the k x − k ysurface crosses Weyl nodes. The order parameter of URu2 Si2 in hidden ordered phase has not been
uncovered. Hence, the hidden order parameter of URu2 Si2 has been investigated. Furthermore,
the topological of chiral d-wave superconducting state of URu2 Si2 has not been fully understood.
Therefore, we examined the topological properties by
calculating the Chern number, energy spectrum and thermal Hall conductivity. For various magnitudes of the ratio of the inter-sublattice pairing and intra-sublattice pairing, we clarified topological properties. We found chirality inversion, which means the sign change of Chern
numbers. These changes of Chern numbers indicate appearance of a new kind of Weyl points. Moreover, when
Figure 1: Relation between k z and Chern
number. Influences of the hidden order are the influences of the hidden order are considered Fermi
considered. There are some points where surface is deformed and odd Chern number −1 or 3 isthe Chern number changes. These changes
found. Hence, we conclude that hidden ordered phase
imply that the Weyl nodes exist there.
changes the configuration of Weyl points.

[1] S. Kittaka et al, J. Phys. Soc. Jpn. 85, 033704 (2016).
[2] K. Yano et al, Phys. Rev. Lett. 100, 017004 (2008).
[3] M. Sato and S. Fujimoto, J. Phys. Soc. Jpn. 85, 072001 (2016).
[4] S. A. Yang et al, Phys. Rev. Lett. 113, 046401 (2014).

95

P53
Spin current correlation in a three terminal quantum dot
R. Sakano1 and A. Oguri2
1Institute for Solid State Physics, The University of Tokyo, Japan
2Department of Physics, Osaka City University, Japan
Observation of current correlations in nano-size conductor elements has brought a rich
physics. For example, shot noise tells us an effective charge of current-carrying particle, and acurrent cross correlation between paths and spin current cross correlations reflect statistics andentanglement of the current-carrying particle, respectively[1-3].
We study current cross correlations in a quantum dot connected to more than three electriclead electrodes in the Kondo regime and the regime with zero electron in the dot. Especially weinvestigate cross correlation of linear and nonlinear spin currents through different electric leadelectrodes and discuss properties of the Bell-state entanglement that emerges between leadelectrodes.

[1] M. Ferrier, RS et al., Nat. Phys. 12, 230-235 (2016).
[2] T. L. Schmidt, A. Komnik, and A. O. Gogolin, Phys. Rev. Lett. 98, 056603 (2007).
[3] RS, A. Oguri, Y. Nishikawa, and E. Abe, arXiv:1810.13032

96

P54
Observation of magnetically combined two-dimensional
electronic states in a layered antiferromagnet EuSn2As2
S. Sakuragi1, R. Sakagami2, K. Kuroda1, C. Bareille1, N. Azuma2, T. Iwatake2,
S. Sasaki3, S. Doi3, N. Tsujimoto3, R. Akashi3, S. Kunisada1, R. Noguchi1,
K. Kurokawa1, T. K. Kim4, C. Cacho4, S. Shin1, Y. Kamihara2, and T. Kondo1
1

2

Institute for Solid State Physics, The University of Tokyo, Japan
Department of Applied Physics and Physico-Informatics, Keio University, Japan3
Department of Physics, The University of Tokyo, Japan
4
Diamond Light Source, UK

Recently, the layered material, which is composed of layered two-dimensional materials byvan der Waals force, attracts attention by the standpoint from the developing of the novel
functionally materials. In this system, we can configure and control the electronic property,
optical property, and spin orbit coupling by choosing the properties of each layers. From thisstandpoint, we study EuSn2As2, which is composed ferromagnetic two-dimensional Eu layerand double SnAs layer.
In EuSn2As2, the Eu spins are coupled antiferromagnetically across adjacent layers, and theNeel temperature is ~25 K. From the transport measurement, the increasing in the resistivity of
EuSn2As2 below Neel temperature is observed. The angle resolved photoemission
spectroscopy measurement shows the three-dimensional band dispersion above Neeltemperature around Γ point. This band dispersion changes to two-dimensional below Neeltemperature, and the transition of the Fermi surface is occurred. The first-principle calculation
well reproduces this transition of the electronic states. This result shows that the magnetic
ordering of the Eu spins modifies the dimension of the electronic system and affects thetransport property. Our findings suggest that the magnetic ordering affects the bandengineering via developing of the layered materials, opening the possibility of tailoring
magnetoresistance by appropriate structural electronic engineering.
[1] H. Masuda et al., Science Adv. 2, e1501117 (2016).
[2] M. Q. Arguilla et al., Inorg. Chem. Front. 4, 378 (2017).
[3] R. Sakagami, et al., Mater. Sci. Tech. Jpn. 55, 72 (2018).

97

P55
Surface acoustic wave on natural and artificial multiferroics.
R. Sasaki1, Y. Ishii1, Y. Nii2, Y.Iguchi3, T. Ito4, and Y. Onose2
1
Department of Basic Science, University of Tokyo,
2
Institute for Materials Research, Tohoku University,
3
Department of Applied Physics, Stanford University,
4
National Institute of Advanced Industrial Science and Technology
Surface acoustic waves (SAWs) are an acoustic wave mode propagating on the surface of themedium. On piezoelectric materials, the SAW can be electrically excited and detected with useof interdigital transducers (IDT), which consists of two interlocking comb-shaped electrodes. The
devices composed of two IDTs on the piezoelectric substrate are widely used as bandpass filtersin many electronic devices such as cellphones.
Multiferroics are a class of materials, in which ferroelectricity and magnetism coexist. The
strong electromagnetic coupling in multiferroics gives rise to novel phenomena such as
nonreciprocal directional dichroism. When the substrate of SAW devices is replaced bymultiferroic materials, interesting magnetoelectric responses are expected.
Here we investigated SAW propagation on artificial and natural multiferroics.
We have found that the SAW signals are largely modulated by magnetic fields for thesematerials. In ferromagnetic/piezoelectric hybrid device Ni/LiNbO3, which can be viewed as theartificial multiferroics, we observed nonreciprocal propagation of SAW: the absorption and phasevelocity are dependent on the sign of the wave vector [1]. In multiferroic materials BiFeO3 andCuB2O4, piezoelectricity and magnetic order coexist. We successfully excited SAW by utilizing
piezoelectricity of BiFeO3 and observed the intensity and the velocity modulation by the magnetic
field [2]. In the CuB2O4 SAW device, we observed SAW propagation coupled toantiferromagnetic resonance[3].

Nonreciprocal SAW propagation [1]First SAW excitation on

SAW coupled toMultiferroics [2]Antiferromagnetic resonance [3][1] R. Sasaki, Y. Nii, Y. Iguchi, and Y. Onose, Phys. Rev. B 95, 020407 (2017).
[2] Y. Ishii, R. Sasaki, Y. Nii, T. Ito, and Y. Onose, Phys. Rev. Appl. 9, 034034 (2018).
[3] R. Sasaki, Y. Nii, and Y. Onose, arXiv:1811.01527v1.

98

P56
Control of electron spin through quantum Hall edge-spin
entanglement
T. Shimizu1,2 , Y. Hashimoto1 , T. Nakamura1 , A. Endo1 , and S. Katsumoto1,2
1 Institute for Solid State Physics, The University of Tokyo, Japan
2 Department of Physics, The University of Tokyo, JapanThe electron correlation eﬀect brings about spin-separation of the quantum Hall states (quantum
Hall ferromagnets). In such situation, the kinetic motion (edge state) and the spin have maximal
entanglement through which the spin can be manipulated. However, only a limited number ofexperiments have been reported on that due to the diﬃculty in introducing non-adiabatic interedge transition[1][2]. Here we demonstrate that electron filling factor and spatial shaping of edges
strongly aﬀect the controllability of spins.
The sample configuration is shown in Fig.1. Five Au/Ti gates were fabricated onto an edge ofa two-dimensional electron system (2DES) in an AlGaAs/GaAs heterostructure with the mobilityof 90 m2 /Vs. We cooled the sample down to 30 mK and applied perpendicular magnetic field B
up to 9 T, at which the 2DES is in the quantum Hall state with the filling of ν = 2. Under the Gate
L and R, the electron concentration was reduced to νL, νR = 1 for separation of the spin-polarizededge states. One edge state which goes through the νR = 1 region meets the others at the lower
right corner of Gate SR. At a sharp corner in the electron orbit, the Landau-Zener tunneling brings
about non-adiabatic inter-edge channel transition for some portion of electron wavefunction andthe electron spin starts precession alongside Gate C. The spin state at the left corner of Gate SL
is measured by current distribution ratio D = IL /(IL + IB ). Fig.2 shows B and Gate C voltage
dependence of D, which shows oscillation in both direction of the axis. This means that wecontrolled spin precession with Gate C voltage.
[1] T. Nakajima, K.-T. Lin, and S. Komiyama, AIP Conf. Proc. 1566, 301 (2013).
[2] B. Karmaker et al., Phys. Rev. B 92, 195303 (2015).

Figure 1: Optical micrograph of thesample and terminal configuration.

Figure 2: Gate C voltage and magnetic field dependence of current distribution D = IL /(IL + IB ).

99

P57
Quadrupolar Kondo Effect in Magnetoresistance ofNon-magnetic Γ3 System PrV2Al20
N. Sogabe1, A. Sakai1, M Tsujimoto1 and S. Nakatsuji1
1
Institute for Solid State Physics, The University of Tokyo, Japan
PrTr2Al20 (Tr: Ti,V) is known to be one of the first example of quadrupole Kondo latticesystem; namely, the crystalline electric field ground state is the nonmagnetic cubic 3 grounddoublet and clear c-f hybridization is observed [1-3] Nonmagnetic order is observed at TQ = 2.0
K (Ti) and 0.75 K, 0.65 K (V) due to the ferro- and antiferro- quadrupole order, respectively. [1,2, 4] In addition, superconductivity is observed at Tc = 0.2 K (Ti) and 0.05 K (V) [4, 5], and heavy
fermion superconductivity with the enhanced T c = 1 K (Ti) is found under the hydrostatic pressureof 8 GPa. [6] Comparing PrV2Al20 with PrTi2Al20, PrV2Al20 shows much stronger c-f
hybridization effect. Indeed, PrV2Al20 exhibits anomalous metallic behavior in resistivity  ~√𝑇,
magnetic susceptibility  ~ − √𝑇, and specific heat C ~ 𝑇 −1/2 , while PrTi2Al20 exhibits ordinary
Fermi liquid behavior. [1] Although the origin of this anomalous metallic behavior in PrV2Al20 is
most likely due to the quadrupole Kondo effect, there is still lack of clear evidence.
Here, we report the magnetic and quadrupole Kondo effect in PrV2Al20 based on themagnetoresistance, magnetic susceptibility and specific heat measurement, and discuss the originof the anomalous metallic behaviors of PrV2Al20.
[1] A. Sakai and S. Nakatsuji: J. Phys. Soc. Jpn. 80 (2011) 063701.
[2] T. J. Sato, S. Ibuka, Y. Nambu, T. Yamazaki, T. Hong, A. Sakai, and S. Nakatsuji: PhysicalReview B - Condensed Matter and Materials Physics 86 (2012) 184419.
[3] M.Koseki, Y. Nakanishi, K. Deto, G.Koseki, R. Kashiwazaki, F. Shichinomiya, M.
Nakamura, M. Yoshizawa, A. Sakai, and S. Nakatsuji: J. Phys. Soc. Jpn. 80 (2011) SA049.
[4] M. Tsujimoto, Y. Matsumoto, T. Tomita, A. Sakai, and S. Nakatsuji: Phys. Rev. Lett. 113(2014) 267001.
[5] A. Sakai, K. Kuga, and S. Nakatsuji: J. Phys. Soc. Jpn. 81 (2012) 083702.
[6] K. Matsubayashi, T. Tanaka, A. Sakai, S. Nakatsuji, Y. Kubo, and Y. Uwatoko: Phys. Rev.
Lett. 109 (2012) 187004.

100

P58
Theory of proximity effect in Rashba nanowire junction
D. Takagi, Y. Tanaka,
Dept. of App. Phys, Nagoya Univ., Japan
Superconductiong proximity effect is a phenomenon in which Cooper pairs penetrate into N(normal metal) at N / S (superconductor) junction. Then, local density of states (LDOS) in N has
a gap like structure around zero energy. At DN (diffusive normal metal) / S (spin-triplet) junction,
however, LDOS in DN has a zero energy peak (ZEP) and a zero bias conductance peak (ZBCP) is
quantized. The phenomenon is anomalous proximity effect.

(a)

(b)

(c)

ρ(ε)

ρ(ε)

µ/t = 0
1

G N S [2e2/h]

LDOS

LDOS

1

1

0.8

L = 100.6
0.4

L = 200.2

0−0.3Energy0 ε/∆

00.3 −0.3
0.3
0Energy ε/∆

0
−1

−0.5

0

0.5

1

eV /∆

Figure 1: While LDOS has a gap like structure in conventional proximity effect (Fig .1(a)), there is a ZEP
of LDOS in anomalous proximity effect (Fig. 1(b))[1]. Behavior of a quantized zero bias conductance(Fig. 1(c))[2].

The zero energy states in anomalous proximity effect is Majorana fermion. It is a quasiparticleof which creation and annihilation are identical. The application of it is quantum computation. It
is revealed that Majorana fermion accompanies odd-frequency pairing[3].
Kitaev chain is a one-dementional spinless px -wave superconductor. However, it has not beenachieved yet. The model which is more realistic than Kitaev chain is a nanowire with Rashba
spin-orbit coupling and Zeeman field proximately coupled to a spin-singlet s-wave superconductor(Rashba nanowire system). It is effectively equivalent to Kitaev chain at low energy.
Although proximity effct at Rashba nanowire junction is calculated with Recursive Green’s
funciton[3], the spacial dependence and symmetry of Cooper pairs is not revealed yet. In thistalk, we discuss the change of the spacial dependence and symmetry of Cooper pairs from the
topological regime to the non-topological regime by tuning chemical potential.

[1] Y. Tanaka, A. A. Golubov, Phys. Rev. Lett. 98, 037003 (2007).
[2] D. Takagi, S. Tamura, Y. Tanaka, arxiv: 1809.09324 (2018).
[3] Y. Asano, Y. Tanaka, Phys. Rev. B 87 104513 (2013).

101

P59
Fabrication and Evaluation of Magnetic TopologicalInsulator Heterostructure MnTe/(Bi1-xSbx)2Te3
T. Takashiro1, R. Akiyama1, I. A. Kibirev 2,3, A. V. Matetskiy 2,3, H. Toyama1,
A. V. Zotov2,3, A. A. Saranin2,3, and S. Hasegawa1
1
Department of Physics, The University of Tokyo, Japan
2
Institute of Automation and Control Processes FEB, Russia
3
School of Natural Sciences, Far Eastern Federal University, Russia
Inducing magnetism into topological insulators (TIs) causes intriguing exotic phenomena
such as the quantum anomalous Hall effect (QAHE), which is promising for spintronics due tothe dissipation-less edge current. To realize QAHE, it is necessary to open a gap in the surfaceband, Dirac cone, and tune the Fermi level (EF) within the gap. A lot of reported studies havefocused on doping magnetic impurities into TI to open the gap. However, due to obstacles suchas magnetic scattering or inhomogeneous magnetism, the QAHE has been observed still onlyat very low temperature (10 - 100 mK).
Previously,
wereported
Bi2Se3includingaself-assembled
ferromagnetic Mn single layer on aSi(111) substrate by MBE , andconfirmed the gap opening [1]. However,EF was not located in the gap so that it
was difficult to observe the QAHE. On
the other hand, it is known that EF in(Bi1-xSbx)2Te3 can be tuned to be both nFigure 1. E-k dispersion images by ARPES of (a)and p types by changing the(Bi0.11Sb0.89)2Te3 and (b) MnTe/(Bi0.11Sb0.89)2Te3 at 77 K.
concentration x [2]. In this study, we
The inset of (b) shows momentum-distribution curves
have
grown
MnTe/(Bi1-xSbx)2Te3(MDCs) at the respective energy ranges near EF represented
by the blue dashed square.
(MnTe/BST) and aimed to fabricate ahigh-quality topological magnetic heterostructure and to tune EF within the gap. Because
depositing MnTe induces holes, which was confirmed by the Hall effect also, we planned totune EF of BST toward the conduction band side initially as shown in Fig. 1(a), then expected
EF to lie at the Dirac point after deposition of MnTe. The resultant optimized x = 0.89, and the
ARPES image of the band dispersion shows that the Dirac point is just the same energy as EF
as shown in Fig. 1(b) and the inset. Additional and more detailed data containing magnetic andtransport measurements will be shown in my presentation.
[1] T. Hirahara et al., Nano Lett. 17, 3493 (2017).
[2] J. Zhang. et al., Nat. Commun. 2, 574 (2011).

102

P60
Pressure induced phase transition on a frustrated squarelattice spin system RbMoOPO4Cl
H. Takeda1, T. Yamauchi1, M. Yoshida1,2, M. Takigawa1, H. Ishikawa1,3 and Z. Hiroi1
1
Institute for Solid State Physics, The University of Tokyo, Japan
2
Max-Planck Institute for Solid State Research, Germany
3
University of Stuttgart, Germany
For past a few decades, great efforts have been devoted to search nontrivial quantum
disordered states in the magnetically frustrated systems[1]. Geometrically frustrated magnets
with triangular or Kagome lattices are one of the target materials. Since the competition of theequivalent exchange interactions arises the frustration, perfectness is required in the latticegeometry to realize the disordered phases. This point prevents us to find out the disorderedphases. Another type frustration appears in the competition between inequivalent exchangeinteractions, such as the nearest neighbor J1 and the next nearest neighbor J2 exchangeinteractions. The disordered phases in these systems seem more favorable to tolerate thestructural distortions, since relatively wide values of J2/J1 preserve strong magnetic frustrations.
Frustrated square lattice magnets are one of such systems, where three ordered phases,
Columnar-type (CAF) and Neel-type (NAF) antiferromagnetic and ferromagnetic (FM) ones
could be realized as a result of competition of the exchange interactions J1 running along theside of the square and J2 running to the diagonal[2,3]. At the intermediate region between the
CAF and NAF phases around J2/J1~ 0.5, the long range order would be suppressed and spin
liquid phase is expected to appear. Although several vanadium and molybdenium compounds
have been synthesized[2,3], all materials investigated so far exhibit antiferromagnetic orders
with NAF or CAF type spin alignments at ambient pressure.
In this study, we demonstrate the pressure effect on magnetism of a spin-1/2 frustrated
square lattice magnet RbMoOPO4Cl, which undergoes the CAF type antiferromagnetictransition at ~TN=8 K at ambient pressure[4]. Application of hydrostatic pressure controls thestrength of magnetic exchange interactions, resulting in a pressure induced phase transition
from the CAF spin alignment at ambient pressure to the NAF one above ~3.5 GPa. The
structural distortion in MoOPO4 layer would play an important role for tuning the exchangeinteractions. At the phase boundary there is intermediate region of phase coexistence between
the CAF and NAF phases, which implies that the phase transition is a first order transition.
The absence of disordered phase in this material may be associated with the exchange
anisotropy which destabilizes the spin liquid phase[5].
[1]L. Savary and L. Balents, Rep. Prog. Phys. 80, 016502 (2017)., [2]R. Nath, et al., Phys. Rev.
B 80, 214430 (2009)., [3]L. Yang, et al., Phys. Rev. B 96, 024445 (2017)., [4]H. Ishikawa, etal., Phys. Rev. B 95, 064408 (2017)., [4] R. F. Bishop, et al., Phys. Rev. B 78, 054412 (2008).

103

P61
Observation of collective phonon mode in quantum spinorbital liquid Ba3CuSb2O9 using time-resolved resonant
soft x-ray scattering
K. Takubo1, K. Yamamoto1, Y. Hirata1, H. Wadati1, H. Man1, S. Nakatsuji1
1
Institute for Solid State Physics, The University of Tokyo, Japan
Ba3CuSb2O9 is a candidate for quantum spin-orbital liquid [1-3]. Although the octrahedral
Cu site is expected to be 2+(d9, s=1/2), the hexagonal Ba3CuSb2O9 does not show any static
Jahn-Teller distortion or orbital order as well as the spin order at the lowest temperature (<20mK) owing to the geometrical frustration. On the other hand, orthorhombic Ba3Cu1-xSb2+xO9shows an orbital and spin order below 200 K. We studied photo-induced dynamics on the Cusites of Ba3CuSb2O9 by means of time-resolved resonant soft x-ray scattering (Tr-RSXS) at theCu L3 absorption edge. Tr-RSXS were measured using a Tr-RSXS and XAS system at theBL07LSU of SPring-8 which were developed by us recently [4].
Figure 1 shows time evolution of the Tr-RSXS intensity Q=(002) at the Cu L3 edge
(hv=930.2 eV). The intensity of RSXS reflects
x-ray 923 eV
the Jahn-Teller fluctuation (or diffusive state) of
the Cu 3d electronic state at the low temperature.
A coherent oscillation ~165 ps is observed on
the photo-induced dynamics for hexagonal
Ba3CuSb2O9, which is similar to a characteristicfrequency observed on the ESR experiment
below 40 K [5]. On the other hand, theorthorhombic Ba3Cu1-xSb2+xO9 does not exhibit
the distinct oscillation. Namely, this slow andlong-lived coherent oscillation will correspondto the characteristic frequency or ‘collective
phonon mode’ of the spin-orbital fluctuation in
the Cu sites of Ba3CuSb2O9.

Figureintensity Q=(002) for hexagonl Ba3CuSb2O9(upper) and orthorhombic Ba3Cu1-xSb2+xO9(lower).

[1] S. Nakatsuji et al., Science 336, 559 (2012).
[2] T. Ishiguro et al., Nat. Commun. 4, 2022 (2013).
[3] N. Katayama et al., PNAS 112, 9305 (2015).
[4] K. Takubo et al., Appl. Phys. Lett. 110, 162401 (2017).
[5] Y. Han et al. Phys. Rev. B 92, 180410 (2015).

104

1: Time-evolution of Tr-RSXS

P62
Realization of spin nematic phases in antiferromagnetic
dimer dumbbell models on two-dimensional lattices
K. Tanaka and C. Hotta
Department of Basic Science, University of Tokyo, Japan
Dimer dumbbell arrangement of spins has oﬀered a variety of quantum phases, such as theobservation of magnon crystallization in Ba2 CoSi2 O6 Cl2 [1], and the experimental proposal ofa quantum spin liquid state in Ba3 ZnRu2 O9 [2]. We have recently proposed that on a triangularlattice consisting of dimer dumbbells constructed by two spin-1/2 interacting antiferromagnetically,
ring-exchange or four-spin exchange interactions across two dimers trigger spin nematic orders
in the vicinity of an ordinary dimer singlet phase [3]. When triplet dimers are eﬃciently doped
and occupy the adjacent two dimers, the ring-exchange interactions among four spin-1/2 (twotriplets) work as spin-1 biquadratic interactions between them. Such interactions are obtained by
fourth-order perturbation processes in Mott insulators, and could take a reasonably large value [4].
In usual spin models, the phases of spin-1/2 and spin-1 systems are completely diﬀerent.
However, by replacing the spin-1/2 pairs of dumbbells with spin-1 pairs, we show that the system
can be mapped onto a similar model to the spin-1/2 system in certain cases (Fig. 1). Although
the ground state should again be a singlet phase, there would be other exchange interactions as
the aforementioned spin-1/2 case. We will discuss the relation between these interactions and thefeasibility of spin nematic phases in spin-1 dimer systems.

Fig. 1: A schematic image of spin-1 dimer dumbbell models on a two-dimensional lattice.

[1] H. Tanaka et al., J. Phys. Soc. Jpn. 83, 103701 (2014).
[2] I. Terasaki et al., J. Phys. Soc. Jpn. 86, 033702 (2017).
[3] Y. Yokoyama and C. Hotta, Phys. Rev. B 97, 180404(R) (2018).
[4] K. Tanaka, Y. Yokoyama, and C. Hotta, J. Phys. Soc. Jpn. 87, 023702 (2018).

105

P63
Metamagnetism, Criticality and Dynamics in the
Quantum Spin Ice Pr2Zr2O7
N. Tang 1, A. Sakai 1, K. Kimura 2, S. Nakamura 3, Y. Matsumoto 4, T. Sakakibara 1, S.
Nakatsuji 1
1
Institute for Solid State Physics, The University of Tokyo, Japan
2
GSFS, The University of Tokyo, Japan
3
Nagoya Institute of Technology, Japan
4
Max Planck Institute, Germany
Geometrical frustration may prevent the formation of long-range magnetic order, giving
rise to a diverse range of novel ground states. One of such an unusual state is called quantum
spin liquid (QSL) possibly realized in quantum spin ice systems. Its excitations behave likecharged particles interacting with linearly dispersive “photon”, protected by hidden topologicalorder parameter. Yet, the properties of quantum phase transition between such topologicalphases remain unknown and are waiting to be established.
Pr-based pyrochlore compounds such as Pr2Ir2O7 and Pr2Zr2O7 are known to be quantum
spin ice systems. Pr2Ir2O7 is a fascinating material exhibiting various exotic phenomena suchas the spontaneous anomalous Hall effect [1]. In contrast to Pr2Ir2O7, the insulating Pr2Zr2O7
renders a simplified platform to explore the physics of quantum spin ice. K. Kimura et al. [2]reported the absence of “pinch points” in the inelastic neutron scattering spectrum of Pr2Zr2O7,
suggesting the breakdown of the ice rule owing to quantum fluctuations — a promising hint ofa U(1) QSL state. In a recent study [3], it was found that structural disorder acts as a transverse
field on the non-Kramers Pr3+ ion in Pr2Zr2O7, stabilizing the QSL state. Under a magnetic
field along the [111] axis, classical spin ice materials undergo a first-order metamagnetictransition [4]. Although theoretical studies [5] predict the existence of metamagnetic transitionin quantum spin ice, a comprehensive experimental investigation is still lacking. Here, wereport magnetization, thermal expansion, and magnetostriction measurements on Pr2Zr2O7.
These measurements aim to clarify the nature of the metamagnetic transition and to probepossible topological quantum criticality.
[1] Y. Machida et al., Nature 463, 210 (2010) [2] K. Kimura et al., Nature Commun. 4, 1934
(2013) [3] J.-J. Wen et al, PRL 118, 107206 (2017) [4] T.Sakakibara et al., PRL 90, 207205 (2003)[5] T.A. Bojesen, and S.Onoda, PRL 119, 227204 (2017)

106

P64
Superconductivity near a ferroelectric quantum criticalpoint in La-doped SrTiO3
Y. Tomioka, N. Shirakawa, K. Shibuya, and I. H. Inoue
National Institute of Advanced Industrial Science and Technology (AIST),
Tsukuba 305-8565, Japan

16

1-x

C

16

Resistivity [µcm]

x

18
1-z

z 3

C

1-x

x

18
1-z

z 3

C

Critical temperature, Tc (K)Resistivity [µcm]

In this paper, we report an increase of the superconducting transition temperature TC upon theoxygen isotope (18O) substitution for La-doped SrTiO3 single crystals prepared by floating zone
method. Figure 1 shows the resistive transitions [(a), (b)] and the evolution of the criticaltemperature TC (c) for the normal and enriched Sr1-xLaxTi(16O1-z18Oz)3 crystals. In Fig. 1(a) and
1(b), TC increases upon the substitution of normal oxygen with the 18O, and it exceeds 500 mK
for the crystal with x = 0.0035
400
(a)
0.7
(c)
and z = 0.57 (b). In the insulating
Sr La Ti( O
O)
300
z=0
T = 0.38 K
0.6
single crystals
0.0035
SrTiO3, the quantum paraelectric200
z = 0.57
0.002; SrTiOT = 0.5 K
0.5(Schooley et al.)0.0035100
state is changed to a ferroelectric
0.002
0.4
x = 0.002
0.003
0state when the normal oxygen is
0.001
0.005
0.001
Sr La Ti( OO)
0.007
0.0005
300
0.3
0.009
replaced with the 18O by ~36 %
z=0
0.01
16
18
0.2
200
T = 0.44 K[SrTi( O1-z Oz)3 (z ≥ 0.36)] [1].
0.01
; z = 0, Verneuilz = 0.57; z = 0, FZ
T = 0.55 K; z ~ 0.6
0.1
The enhancement of TC in Fig. 1
100
0.042
x = 0.0035(b)seems to be due to an increased
0
0
10
10
10
10
0
0.2 0.4 0.6 0.8
1carrier density, n (cm )Temperature [K]ferroelectric fluctuation near aferroelectric quantum criticalFigure 1. Superconducting transition temperatures Tc
point at (x, z) = (0, 0.36). With measured using a 3He/4He dilution refrigerator below 1 K
use of the phenomenologicalfor the normal (z = 0) and enriched (z ~ 0.6) crystals oftheory [2], the tunnelling energy Sr1-xLaxTi(16O1-z18Oz)3 with x = 0.002 (a) and 0.0035 (b).
relevant to the ferroelectric (c) Tc vs. n for the Sr1−xLaxTi(16O1−z18Oz)3 single crystals
instability is compared among
together with the Tc for SrTiO3−δ [3] and La-substituted
3-

C

18

19

20

21

-3

SrTiO3-d [3], (Sr,Ca)TiO3-d, SrTi1and Sr1-xLaxTi(16O1xNbxO3,
18z Oz)3.

SrTiO3 [4]. The solid (partially dashed) lines wereobtained from calculations based on the model in Ref. [2].

[1] M. Ito and R. Wang, Appl. Phys. Lett. 76, 221 (2000).
[2] J. M. Edge, et al., Phys. Rev. Lett. 115, 247002 (2015).
[3] J. F. Schooley, et al., Phys. Rev. Lett. 14, 305 (1965).
[4] H. Suzuki, et al., J. Phys. Soc. Jpn. 65, 1529 (1996).

107

P65
Applications of Electron Hydrodynamics to
Nonlocal and Nonlinear Optical Effects
R. Toshio1, K. Takasan1 and N. Kawakami1
1
Department of Physics, Kyoto University, JapanThe conventional theory of optical responses in metals has been based on the
Drude theory, which relies on the assumption that electron-electron scattering is weakenough to ignore and the transport is governed by collisions with defects or phonons.
However it has become possible, in recent years, to prepare ultrapure metallic samples,such as PdCoO2 [1], graphene [2], and GaAs/AlGaAs heterostructures [3], where theelectron-electron scattering becomes most dominant process governing transport andthus the Drude theory is no longer valid. This regime is called ”hydrodynamic regime”
and described by an emergent hydrodynamical theory [4]. In fact, several observationsof hydrodynamic effects in DC transport have already been reported[1, 2, 3].
In this work, we provide a new framework of optical response in hydrodynamic
regime. Based on momentum relaxing Navier-Stokes equation, we calculated theoptical conductivity and regflectivity of 2D and 3D electron fluids and discuss how
electromagnetic waves propagate in electron fluids. Consequently, we revealed that, inthree-dimensional electron fluids, an electromagnetic wave propagates in two modes
due to the nonlocality of electron fluids, which is in constrast with the Drude theory,
where it propagates in only one mode. We further discuss the second harminic
generation resulting from the nonlinearlity of electron fluids.

Figure 1: Schematic picture of optical responses in electron fluids. In the hydrodynamic regime, apropagating wave consists of two different transvarse waves and one longitudinal wave (plasmamode). The nonlinearlity of electron fluids causes second harmonic waves and even higher ones.

[1] Philip J. W. Moll, Pallavi Kushwaha, et al, Science 351 (2016) 1061.
[2] D. Bandurin, I.Torre, et al, Science 351 (2016) 1055.
[3] L. W. Molenkamp and M. J. M. de Jong, Phys. Rev. B 49 (1994) 5038
[4] A. V. Andreev, S. A. Kivelson, and B. Spivak, Phys. Rev. Lett. 106 (2011) 256804

108

P66
Spontaneous Hall effect in all-in all-out Weyl semimetalof pyrochlore iridate
K. Ueda1, R. Kaneko1, H. Ishizuka1, J. Fujioka1,2, N. Nagaosa1,3, and Y. Tokura1,3
1
Department of Applied Physics, The University of Tokyo, Japan
2
PRESTO, Japan Science and Technology Agency, Japan
3
RIKEN Center for Emergent Matter Science (CEMS), Japan
Topological quantum states of matter, characterized by geometrical features of electronic
band structures, have been extensively explored and studied1. Among them, the topologicalelectronic state with magnetic order or broken time-reversal symmetry remains elusive becauseof a scarce number of examples. Here we present experimental observations proving that the
pyrochlore iridate, when electronically tuned, can be a topological Weyl semimetal as
predicted theoretically2. By tracking transport measurements, we observe a sizable
spontaneous Hall conductivity with minimal magnetization only within a few Kelvin below the
all-in all-out magnetic ordering temperature as shown in the figure. Our theoretical calculation,
which is quantitatively consistent with the observation, suggests that the presence of linearlydispersing crossing points (Weyl points), acting as a source/sink of a quantized magnetic fluxin k-space, potentiallygives rise to such anenormous effect. The
manifestation of thesalient Hall response
provides one important
example of topologicalstates, which promotes
a better understandingof Weyl semimetal andindicatesthenewresearch direction forthetopologicalmaterials design andfunction.
Phase diagram and representative magnetic transport
properties in R2Ir2O7.

[1] Hasan, M. Z. & Kane, C. L. Rev. Mod. Phys. 82, 3045 (2010).
[2] Wan, X., Turner, A. M., Vishwanath, A. & Savrasov, S. Y. Phys. Rev. B 83, 205101(2011).

109

P67
Strong-correlation induced highly mobile electronsin Dirac semimetal of perovskite CaIrO3
R. Yamada1, J. Fujioka2,3, M. Kawamura4, T. Okawa1, S. Sakai4,
M. Hirayama4, R. Arita1,4, D. Hashizume4, M. Hoshino2,4 and Y. Tokura1,4
1
Department of Applied Physics, The University of Tokyo, Japan
2
PRESTO JST,
3
Department of Applied Physics, The University of Tsukuba, Japan
4
RIKEN CEMS
Topological semimetals have been attracting significant attention because they show uniquequantum transport properties derived from highly mobile Dirac/Weyl fermions such as giant
magneto-resistivity and chiral anomaly. So far, these properties have been observed mainly in
weakly correlated systems such as Cd3As2[1] and Na3Bi[2]. On the other hand, it is theoretically
predicted that topological semimetallic state can be realized in strongly correlated materials. For
example, the possible realization of a magnetic Weyl semimetal phase has been proposed inpyrochlore-type iridates[3], wherein correlated Weyl electrons manifest themselves as the giant
magnetoresistivity and anomalous Hall effect. Another example is the Dirac semimetal phase inperovskite-type AIrO3 (A=Ca,Sr)[4] with Dirac nodal-line protected by nonsymmorphic crystalline
symmetry, wherein the conduction band and valence band cross along a closed line in momentum
space as shown in Figure(a). However, the quantum transport associated with highly mobile
Dirac/Weyl fermions have been rarely observed in these classes of strongly correlated topologicalsemimetals.
In this study, we report the unique quantum transport phenomena of correlated Dirac electronin perovskite CaIrO3[5]. We found that the highly mobile electrons exceeding 60,000cm2/Vs with
the quantum oscillation emerging at low temperature. Combined with ab-initio calculations, weconclude that the interplay between electron correlation and spin-orbit interaction causes theremarkable proximity of Dirac node to the Fermi energy, yielding the highly mobile electrons.
(a)

(b)

(a) Band structure around Dirac nodal-line. (b) Quantum oscillation observed in longitudinalmagnetoresitivity.
[1] T. Liang et al., Nat. Matter. 14, 280 (2015) [2] J. Xiong et al., Science 350, 6259 (2015)[3] K. Ueda et al., PRL 115, 056402 (2015) [4] M. Zeb and H. Kee, PRB 86, 085149 (2012)[5] J. Fujioka, R. Yamada et al., submitted.

110

P68
Fate of loss-induced superconductivity studied by
non-Hermitian mean field theory
Kazuki Yamamoto1 , Norio Kawakami1
1 Department of Physics, Kyoto University

When we consider the eﬀects of dissipation such as loss of particles or inelastic scattering,
Hamiltonian of the system is no longer Hermitian but could be non-Hermitian because dissipation
may cause non-unitary dynamics of the system, leading to the decay of eigenstates. In recent
years, non-Hermitian quantum systems have been extensively studied both experimentally andtheoretically [1–4]. However, most of the previous studies dealt with systems without interaction
and there have been few studies focusing on quantum many-body phenomena. In this study,
we investigate how the BCS superconductivity, a prototypical example of quantum many-bodyphenomena, changes its character when the eﬀects of dissipation are taken into account. In thepresence of two-particle loss, the attractive potential forming Cooper pairs becomes complex.
Such a situation can be realized experimentally, for example, as the Orbital Feshbach Resonance(OFR) where the interaction between the ground 1 S0 state and excited 3 P0 state in ultracold
alkaline-earth atoms becomes complex because of dissipation. Furthermore, as the experiments torealize superfluids using OFR by controlling the interaction between diﬀerent orbitals have been
actively conducted these days, it is particularly important to investigate the stability of superfluids
in the system under dissipation. We calculate the action from the partition function using HubbardStratonovich transformation and neglecting quantum and space fluctuations. Then we obtain the
gap equation for the dissipative superconducting system by taking the saddle point of the action.
We elucidate the fate of Hermitian superconductivity by taking the real part of the gap focusing
on short-time non-Hermitian dynamics: at a critical strength of dissipation (imaginary part ofinteraction), the superconducting gap closes, leading to a breakdown of BCS superconductivity.
We finally show how the BCS mean-field theory in open quantum systems is changed from its
Hermitian one and the corresponding superconducting gap under dissipation is expressed by the
expectation value of fermionic operators.
Acknowledgement: This work is done in collaboration with Kazuaki Takasan (Kyoto Univ.),
Kyosuke Adachi (Kyoto Univ.), Masaya Nakagawa (RIKEN), Masahito Ueda (Univ. of Tokyo &RIKEN).

[1] A. Guo et al. Physical Review Letters 103 (2009) 093902.
[2] Takafumi Tomita et al. Science Advances 3 (2017) e1701513.
[3] Yuto Ashida, Shunsuke Furukawa, Masahito Ueda, Nature Communications 8 (2017) 15791.
[4] Masaya Nakagawa, Norio Kawakami, Masahito Ueda, Physical Review Letters 121 (2018)
203001.

111

P69
Quantum critical phenomena in heat transport
in the subohmic spin-boson system
T. Yamamoto and T. Kato
Institute for Solid State Physics, The University of Tokyo, Japan
Quantum critical phenomena are ubiquitous in condensed matter physics. Recent
technological progress has enabled to realize nanostructures and observe quantum criticalphenomena via electric transport in mesoscopic systems[1]. This success encourages further studyof quantum critical phenomena in different types of transport in well-controlled mesoscopic
systems.
Heat transport via nanostructures is another important topic in mesoscopic physics. In
particular, heat transport in the spin-boson system is one of the most common and importantmodels for describing a local discrete-level system coupled to bosonic thermal reservoirs (seeFigure 1) and has been studied in a number of theoretical studies[2]. Depending on the spectral
density of the thermal reservoirs, 𝐼(𝜔) ∝ 𝜔 & , the processes of heat transport change. Intriguingly,
the subohmic spin-boson model ( 0 < 𝑠 < 1 ) shows a quantum phase transition at zerotemperature when a coupling strength between the two-state system and thermal reservoirs
becomes critical value.
In the present study[3], we consider quantum critical phenomena in heat transport in thesubohmic spin-boson system. We numerically investigate the temperature dependence of thethermal conductance at the critical point using the continuous-time Monte Carlo simulation[4].
We show that the thermal conductance exhibits distinctive power-law behavior determined by thenature of the quantum phase transition near the quantum critical point. In addition, we present a
scheme for the realization of the subohmic spin-boson model using a superconducting circuit.

Figure 1: Schematic of the spin-boson model composed of a two-state system
coupled to two bosonic thermal reservoirs.

[1] Z. Iftikhar et al., Science 360, 1315 (2018).
[2] T. Yamamoto, M. Kato, T. Kato, and K. Saito, New J. Phys. 20, 093014 (2018).
[3] T. Yamamoto and T. Kato, to be published in Phys. Rev. B; arXiv:1809.03688 (2018).
[4] A. Winter et al., Phys. Rev. Lett. 102, 030601 (2009).

112

P70
Local magnetic excitations in Weyl semi-metals exploredby NMR and NQR spectroscopy.
H. Yasuoka1, R. M. Ranjith1, D. Kasinathan1, T. Kubo2, T. Fujii3, M. Schmidt1,
and M. Baenitz1
1
Max Planck Institute for Chemical Physics of Solids, 01187 Dresden, Germany
2
Department of Applied Physics, Okayama University of Science, Okayama, Japan3
School of Science, University of Hyogo, Hyogo, JAPANThe topological nature in condensed matters is one of the most fascinating areas ofadvanced research in solid state physics. Among them, as is represented by Graphene, somecases of semi-metals have a nontrivial linear dispersion of the band structure touching at the
Fermi energy, forming a Dirac point. Upon breaking the centro-symmetry of crystal and/or thetime reversal symmetry, each Dirac point splits into two points called Weyl points with spin
degeneracy lifted and have a topological nature [1]. The Weyl fermions at these Weyl points
appear as a pair with opposite spin chirality due to strong spin-orbit coupling. For theapplication side, Weyl fermions are expected to be a good candidate for the ultra-high speed
and low energy electronic devices. Beyond that, new physics like anomalous Hall effect (Hallvoltage without field) and chiral anomaly (generate current along field) has been anticipated.
Here, we present microscopic “bulk” properties in several Weyl semimetals, focusing on
those low-lying magnetic excitations. Utilizing NMR and NQR techniques, we made detailed
measurements on the T-dependences of line profiles to extract K(T), νQ(T), and nuclear
relaxation rate (1/T1T), both of which gave us a characteristic feature associated with the Weyl
physics. As a typical example, the results for 1/T1T (T) in TaP and TaAs are presented in
Figure 1. For both cases, there exists a characteristic temperature, T* ≈ 30 K, where therelaxation process has a crossover from low temperature Korringa process for a parabolic bandwith a weak temperature dependence to a high temperature activation type T-dependence. For
TaP, in particular, we observed the T2 behavior above T* which is associated with theexcitations in the nodal structure of Weyl points [2] with a characteristic T-dependence ofhyperfine coupling associated with the Weyl fermions [3]. We will also discuss extended our
results on the Weyl-II semimetals, WP2 and MoTe2.
Fig. 1 Typical T-dependence of
1/T1T in Type-I Weyl semimetals,
TaP and TaAs.
[1] F. Arnold, et.al. Nature Communications 7, 11615 (2016)[2] H. Yasuoka et.al., PRL 118 (2017) 236403[3] Okvatovity et.al., PRB 92, 245141 (2016), Hiropsawa et.al., JPSJ 86 063705 (2017)

113

P71
Creation of skyrmions by surface acoustic waves
T.Yokouchi1 , S.Sugimoto2, B.Rana1, S.Seki1, N. Ogawa1, S. Kasai2, Y. Otani1,3
1
RIKEN Center for Emergent Matter Science (CEMS), Japan
2
National Institute for Materials Science (NIMS), Japan
3
Institute for Solid State Physics, The University of Tokyo, Japan
Skyrmion, nanometric topological spin texture, gives rise to various unique physicalphenomena. Especially, because of ultralow current driven motion of skyrmion, skyrmion isconsidered as a promising candidate for an information bit in new magnetic storage devices[1,2]. Recently, the formation of Neel-type skyrmion (Fig. 1) at room temperature is reported
in multilayer thin films in which magnetic metal is sandwiched by two heavy metals [2,3].
This has accelerated the research on the development of skyrmion-based storage devices. In
particular, the creation of skyrmion by external stimuli is one of the most important element inorder to realize the skyrmion-based storage devices. So far the creation of skyrmions has been
demonstrated by employing local spin-orbit torque arising from deliberate geometrical shapesof multilayer films [3,4]. However, these methods are not exactly suitable for integrated
nanoscale devices because the geometric structures designed for the skyrmion creation
occupies a large area.
In this presentation, we demonstrate a novel mechanism for the creation of skyrmion,that is, surface acoustic waves induced skyrmion creation. A stack of Pt/Co/Ir was depositedon LiNbO3 substrate and surface acoustic waves were excited by using interdigital transducers(IDTs). We used a Kerr microscope in polar geometry to observe magnetic structures. Whenthe surface acoustic wave is excited in the ferromagnetic state, skyrmions appear, whichindicates surface acoustic waves creates skyrmions. To clarify the mechanism for the skyrmion
creation induced by surface acoustic waves, we
performed micromagnetic simulation, finding thatmodulated magnetic anisotropy arising from thesurface acoustic waves locally reverses spins and thereversed spins subsequently grow into the core of
Neel-type skyrmion. Our results offer a novel guiding
principle for a means to create skyrmions in ultrathin
films.

Figure 1 Neel-type skyrmion[1] N. Nagaosa and Y. Tokura, Nat. Nanotech. 8, 899 (2013).
[2] A. Fert, V. Cros and João Sampaio, Nat. Nanotech. 8, 152 (2013).
[3] W. Jiang et al., Science 349, 283 (2015).
[4] F. Büttner et al., Nat. Nanotech. 12, 1040 (2017).

114

P72
Symmetry-protection of exceptional points
for correlated systems in equilibrium
T. Yoshida1, R. Peters2 N. Kawakami2, and Y. Hatsugai1
1
Department of Physics, University of Tsukuba, Japan2
Department of Physics, Kyoto University, Japan

In this decade, it has been revealed that symmetry enriches topological phases of condensed
matters. For instance, time-reversal symmetry protects the topology of the Z2 insulators in
two- and three-dimensional systems. Z2xZ2 symmetry in the spin-space protects the Haldane
phase of spin-one systems. This diversification is observed even for topological gapless modes
emerging in topological semi-metals.
Along with this great success, the platform of topological phases has extended to nonHermitian systems where a variety of exotic topological states are reported. In particular, in
non-Hermitian systems, Hamiltonian may violate diagonalizability, resulting in the emergenceof exceptional points[1]. The exceptional points do not require any symmetry-protection, andthe emergence of them are theoretically reported even for correlated systems in equilibrium[2,3].
The above two significant progresses naturally lead us to the following question: “What are
new phenomena arising from interplay of symmetry and exceptional points?” We address thisissue in this presentation. Our analysis uncovers the novel topological degeneracies:
symmetry- protected exceptional rings in two dimensions. In the presentation, we show how
symmetry protects these novel topological degeneracies by taking chiral symmetry as an
example.

[1] H. Shen, B. Zhen, and L. Fu, Phys. Rev. Lett. 120, 146402 (2018).
[2] V. Kozii and L. Fu arXiv. 1708.05841.
[3] T. Yoshida, R. Peters, and N. Kawakami , Phys. Rev. B 98, 035141 (2018).
[4] T. Yoshida, R. Peters, N. Kawakami, and Y. Hatsugai, arXiv: 1810.06297.

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P73
Investigation of Ir magnetism in LaMnO3/SrIrO3
superlattices by hard x-ray magnetic circular dichroism
Yujun Zhang1, Liang Wu2, Motohiro Suzuki3, Yasuyuki Hirata1, Kohei Yamagami1,
Keisuke Ikeda1, Kohei Yamamoto1, Xin Liu4, Jinxing Zhang4, X. Renshaw Wang5,
Yuanhua Lin2, Cewen Nan2, Hiroki Wadati1
1
Institute for Solid State Physics, The University of Tokyo, Japan2
Department of Physics, The University of Tokyo, Japan
1
Institute for Solid State Physics, University of Tokyo, Japan
2
State Key Lab of New Ceramics and Fine Processing, School of Materials Scienceand Engineering, Tsinghua University, China
3
JASRI, Japan
4
Department of Physics, Beijing Normal University, China
5
School of Physical and Mathematical Sciences & School of Electrical and Electronic
Engineering, Nanyang Technological University, Singapore
Entanglement and coupling of charge, spin, lattice and orbital degrees of freedom intransition metal oxide (TMO) systems have attracted much attention in recent years [1].
Fabrication and investigation of materials systems with both strong electron correlation andstrong spin-orbital coupling (SOC) are of both scientific and technical interest. Artificiallysynthesized 3d/5d TMO heterostructure or superlattice can be promising candidates to involve
significant correlation and SOC simultaneously [2,3]. In this work we investigated hard X-ray
circulardichroism[(LaMnO3)n/(SrIrO3)n]m/SrTiO3(XMCD)

ofsuperlattices(n=1,2,8; m=24,12,3; named as SL11, SL22 andSL88) at Ir L2,3 edge. All the superlattices show
XMCD signal (as shown in Figure 1) below the[1] Dagotto E. (2005). Science 309(5732): 257-262.
[2] Matsuno J., et al. (2015). Phys. Rev. Lett.
114(24): 247209.
[3] Yi D., et al. (2016). Proc. Natl. Acad. Sci. USA
113(23): 6397-6402.

116

0.01

Ir L3

11.24

11.28

11.32

Photon Energy (keV)
0.015

XMCD (arb. units)

XMCD signal. Sum rule analysis is applied tostrongly modified by interfacial coupling between
3d and 5d TMO layers.

0.02

11.20

confirmed by temperature dependence of theresults indicate that the Ir magnetic moment can be

0.03

0.00

ferromagnetic ordering temperature, which isanalyze the spin and orbital moment of Ir. These

SL11_30K
SL22_30K
SL88_30K
SL11_200K

0.04

XMCD (arb. units)magnetic

SL11_30K
SL22_30K
SL88_30K
SL11_200K

0.010

Ir L2
0.005

0.000

12.80

12.84

12.88

12.92

Photon Energy (keV)

Figure 1. Ir L edge XMCD spectraof the superlattices

P74
Comparison of Spin Hall Angles for Epitaxial andPolycrystalline Platinum Thin Films
Z. Zhu1, T. Higo1,2, J. Kim3, K. Matsumoto1, H. Isshiki1, D. Qu1, K. Kondou3, S.
Nakatsuji1,2 and Y. Otani1,2,3
1
Institute for Solid State Physics, The University of Tokyo, Japan
2
3

JST CREST, JapanRIKEN-CEMS, Japan

Platinum (Pt) is widely used in pure spin current spintronics and one of the most studied spin
Hall material. The first attempt to make a quantitative measurement of the spin Hall angle (θSH)
for Pt was reported by Kimura et al. [1]. However, different values of the θSH have also beenreported by other groups. The origin of the dispersed θSH values has not been understood until
recent experimental report [2], where different polycrystalline Pt resistivity is one of the main
reasons for the spread of θSH values. The contribution of extrinsic spin Hall effect mechanism isenhanced in Pt with larger impurities, leading to a higher θSH value in lower conductivity Pt. On
the other hand, for single crystalline platinum with higher conductance than polycrystalline
platinum, it is ambiguous how θSH values change. To understand the large difference in θSH values,
the effect of crystallinity on θSH values is indispensable. In this work, we have studied both
epitaxial and polycrystalline Pt films to clarify the effect of crystallinity on the spin Hall properties.
In Our study, Pt thin films on both sapphire and Si/SiOx substrates were fabricated using themagnetron sputtering at a substrate temperature of 550°C.
The crystallographic structure of Pt thin films wasmeasured by x-ray diffraction (XRD). Figure 1 shows
XRD patterns of 2θ-θ scan and φ-scan for Pt thin filmon the sapphire substrate. The six-fold symmetry for Pt(002) indicates that the epitaxial Pt is successfullygrown on Sapphire (001).
We then studied the spin Hall magnetoresistance Figure 1: XRD patterns of 2θ-θ scan and(SMR) in the Pt/Co/AlOx multilayers to estimate the θSH φ-scan (inset) for Pt thin film on thesapphire substrate.
for the epitaxial Pt.
[1] Kimura, T., Otani, Y., Sato, T., Takahashi, S., & Maekawa, S., Physical review letters, 98,
156601 (2007).
[2] Sagasta, E., Omori, Y., Isasa, M., Gradhand, M., Hueso, L. E., Niimi, Y., Otani, Y., &Casanova, F., Physical Review B, 94, 060412 (2016).

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Information for participants
TPFC2019, day 1 (Feb. 18)
1. First, resister your attendance at the registration desk (9:15-10:00).
2. At the registration desk, please also pay the banquet fee (4,000 JPY), if you are attending theconference dinner.

TPFC2019, day 2 (Feb. 19)
1. Please register for the day at the registration desk. TPFC symposium is requested to confirm
their attendance every day.
2. The poster preview session will be held concurrently with the extended lunch break. A
complimentary light meal will be provided on the site. Please also note that nearby coffee shop
Tully’s and the restaurants in the Lalaport shopping mall are unfortunately closed on this day.
3. Before the lunch/poster session, group photos will be taken. Please follow the instruction fromthe TPFC organizers.
4. A conference dinner will follow the symposium on this day.

Conference Dinner
The conference dinner will be held on Tuesday evening, February 19, at Comesta (Italianrestaurant) on the first floor of Mitsui Garden Hotel Kashiwano-ha.
http://comestadome.jp/kashiwanoha/ [in Japanese]
Fee: If you join the conference dinner, please pay the banquet fee of 4,000 JPY at theregistration desk on the first day.
Cancellation: If you have expressed your intention to attend the dinner but become
unfortunately unable to attend it, please let us know immediately but no later than Feb 18.
Cancellation notice after this will result in a cancellation charge.
Participation w/o prior reservation: Conversely, if you become able to join the banquet eventhough you previously told us you would not be able to, please let us know as soon as possible.
Some seats are still available.

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Poster preview session
Prior to the poster session, on 19th in 12:20-14:20, a “poster preview session” is scheduled
for each poster presenter to provide a brief introduction on her/his poster using one slide in one
minute.

Poster awards
All poster presenters are the candidates for poster awards. The poster award winners will bechosen by the invited speakers and senior participants during the poster session. The winners
will be announced and celebrated during the conference closing ceremony on February
20 at 5 PM.

TPFC2019, day 3 (Feb. 20)
1. Please register for the day at the registration desk.
2. Please return your name holder when you leave.

119Venue Floor Map(Kashiwa Campus Station Satellite)120

Where to Eat
A wide variety of restaurants and a food court are available on the third floor of the Lalaport
shopping mall http://kashiwa.lalaport.jp/en/shopguide/gourmet.html. The restaurants there openfrom 10:00 or 11:00 to 21:00/ 22:00 (Hours vary from restaurant to restaurant. For details, pleasecheck the website.) Please note that Lalaport will be closed on Tuesday, Feb. 19 for its regular
statutory inspection. We will serve a light meal as lunch for the participants in the Symposium on
Feb. 19.
For breakfast, the restaurant in the Mitsui Garden Hotel serves breakfast. However, we
generally do not arrange breakfasts at the Hotel even if we booked a room for you. You canrequest breakfasts at the Hotel by yourself but there will be an additional fee. For less expensive
breakfast menus, a MacDonald’s and a Tully’s Coffee are located near the hotel/station. You canalso buy boxed meals, sandwiches, rice balls, brewed coffee, etc. at the Lawson and Family Mart
convenient stores. The former is located in front of the Mitsui Garden Hotel and the latter is next
to the train station.

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General information
Directions
To TPFC Symposium Venue (Kashiwanoha Campus Station Satellite of UTokyo)
http://tpfc.issp.u-tokyo.ac.jp/venue.htm*Note: The Symposium Venue is just at the front of the Kashiwanoha-Campus railway stationand next to Mitsui Garden Hotel.

How to Get Around (Public Transportation)
To get around the greater Tokyo area (including the Kashiwanoha Campus area), the best way is
to use public transportation. To figure out the best route to your destination, this online planner
may be helpful: https://world.jorudan.co.jp/mln/
To make things easier, it is highly recommended to buy a prepaid train card, “Pasmo”(http://www.pasmo.co.jp/en/) or “Suica” (http://www.jreast.co.jp/e/pass/suica.html). With thisrechargeable e-card, you don’t have to go through the hassle of buying a ticket every time youchange trains; All you need to do is to scan the card at the gate (on entry and on exit). The train
fare is automatically deducted from the prepaid card’s balance at the station gates.
You can buy a Pasmo card from ticket machines at the Narita Airport/ Airport Terminal 2
Station (http://www.keisei.co.jp/keisei/tetudou/skyliner/us/faq/index.php). To get a new card, youneed to pay a deposit of 500 JPY, which will be refunded together with the remaining balance
when you return the card. The e-card can be used for trains, subways, buses, vending machines,
some shops and convenient stores, and our campus co-op shops and cafeterias.
Suica cards can be bought from ticket vending machines at JR stations. A refundable
deposit of 500 yen is also required. Although the refund of the deposit does not involve any fees,
the refund of the remaining balance on your Suica card requires a service charge of 220 yen(which is deducted from the remaining balance). To avoid payment of this charge, you may want
to use up the full balance on your card before returning a card to the ticket counter. If the balanceis zero, no service fee will be charged but you will still be able to receive the 500-yen deposit.

122

Cash, Credit Cards & ATMs
Although credit cards are increasingly accepted, cash is still the major payment method in Japan.
Indeed, smaller retailers often accept cash only. We therefore would like to advise you to prepare
sufficient cash before arriving at ISSP, especially if you are staying the Kashiwa Guest House,
where your bill must be paid in cash. If needed, you can withdraw cash from an ATM of Japan
Post

Bank

https://www.jp-bank.japanpost.jp/en/ias/en_ias_index.html

or

Seven

Bank

http://www.sevenbank.co.jp/intlcard/index2.html. Before leaving for Japan, please make sure
your credit or debit card is available for use in Japan and check service charges for international
withdrawals.
Around the symposium/workshop venues, you can find ATMs accepting non-Japanesecards in the locations specified below. In addition to these locations, automated teller machinesof Japan Post Bank and Seven Bank accept foreign cards. Unfortunately, you cannot withdraw
cash with your cards issued outside Japan at other domestic banks’ ATMs, including those on
the Kashiwa campus.

Sightseeing
http://tpfc.issp.u-tokyo.ac.jp/sightseeing.htm
If you would like to know where to visit and how to get around in the greater Tokyo metropolitan
areas, you can find a lot of useful resources on the Internet. Here are a couple of useful sites:
http://www.gotokyo.org/en/index.html
https://www.japan-guide.com/e/e2019.html
https://www.lonelyplanet.com/japan/tokyo#interests(Note: We have no affiliation with any of these services or websites.)

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