平 成 ２ ７ 年 度
京 都 大 学 大 学 院 理 学 研 究 科

Ｄ Ｃ ３ 回 生 研 究 発 表 会
要旨集

２０１５年１１月２４日（火）物 理 学 第 一 分 野

物理学第一分野ＤＣ３回生研究発表会
場所：理学研究科５号館 ５階・第四講義室
発表：１５分（別に質問１０分程度）
２０１５年１１月２４日（火）９：００～

目

開始

次

１．Derivation of Stokes’ law without the hydrodynamic equations
伊丹 將人（

９：００）・・・・・

１

２．Shape fluctuation and deformation of biological soft interfaces
伊藤 弘明（９：２５）・・・・・

２

３．Nonlinear analysis of the interfacial layer effects on the surface
capacitances and electro-osmosis in electrolyte solutions
植松 祐輝（

９：５０）・・・・・

３

４．Disorder effects on quantum phase transition of 4He in nanoporous media
小形
悠（１０：１５）・・・・・

４

１０：４０～１０：５０

休憩

５．Mode bifurcation of a chiral asymmetric dumbbell on a vertically vibrated plate
久保 善嗣（１０：５０）・・・・・

５

６．Coherence resonance occurred in oscillatory motion ofa micrometer-sized droplet between electrode needles
栗村朋（１１：１５）・・・・・

６

７．An ultracold Fermi gas with localized impurities in an opticallattice with controllable interaction
小西 秀樹（１１：４０）・・・・・

７

８．Emergent quantum phenomena in inhomogeneous optical lattices
阪井田 賢（１２：０５）・・・・・

８

１２：３０～１３：３０

昼休み

９．Studies on Non-equilibrium Fluctuating Motion as a Rectifier
佐野 友彦（１３：３０）・・・・・
１０．Transition dynamics from macro- to micro-phase separationin asymmetric lipid bilayers
下林９

俊典（１３：５５）・・・・・１０

１１．Density-matrix renormalization group study of quantum spin systems
with Kitaev-type anisotropic interaction
新城 一矢（１４：２０）・・・・・１１

１２．Estimating effective connectivity between brain areas with DCM
新谷 俊了（１４：４５）・・・・・１２

１５：１０～１５：２０

休憩

１３．Kinetic theory for cohesive granular gases with a square well potential
髙田 智史（１５：２０）・・・・・１３
１４．Ejection-Jet cycle: self-sustaining mechanism of turbulent-laminar interface
寺村 俊紀（１５：４５）・・・・・１４
１５．Laser spectroscopic study of an atomic Bose-Hubbard systemwith an atom-number-projection method
中村 悠介（１６：１０）・・・・・１５
１６．Dimer solid-liquid transition in the honeycomb compound Li2-xRuO3JIMENEZ SEGURA, Marco Polo（１６：３５）・・・・・１６

１７：００～１７：１０

休憩

１７．The effect of the confinement into nano-micelles on the liquid crystalline order
坊野 慎治（１７：１０）・・・・・１７
１８．Nuclear Magnetic Resonance Studies on Heavy Fermion Superlattices
山中 隆義（１７：３５）・・・・・１８
１９．Study of thermal Hall effect in a frustrated magnet
渡邊

大樹（１８：００）・・・・・１９

Derivation of Stokes’ law
without the hydrodynamic equations	 	
 Nonlinear Dynamics Group

Masato Itami

Abstract We study the friction coefficient of a macroscopic sphere in a viscous fluid at low Reynolds
number. By combining Kirkwood’s formula and the Green–Kubo formula in large deviation theory, wederive Stokes’ law without explicitly employing the hydrodynamic equations.
© 2016 Department of Physics, Kyoto University	 	
 In equilibrium systems, macroscopic behavior is systematically described by a universal
framework—thermodynamics. On the basis of a microscopic description of equilibrium systems, the principle ofequal a priori probabilities and Boltzmann’s principle reproduce the framework of thermodynamics, which isestablished as equilibrium statistical mechanics. In contrast, there is still no theory describing the general behaviorof non-equilibrium systems beyond the linear response regime. Thus, much effort has been devoted to theinvestigation of steady-state thermodynamics and non-equilibrium statistical mechanics.
When liquids and gases are out of equilibrium but still remain in local equilibrium, their macroscopic
dynamical behavior is precisely described by the hydrodynamic equations. A microscopic understanding of thehydrodynamic equations for the case of dilute gases was established through the Boltzmann equation, whereas it
remains unclear for a general fluid. Non-trivial relations that are generally valid far from equilibrium, including
the fluctuation theorems and the Jarzynski equality, have been developed over the past two decades as a result of
the time-reversal symmetry of microscopic mechanics. Thanks to such universal relations, we can easily re-derivecertain well-known relations, such as the McLennan ensembles, the Green–Kubo formula, and the Kawasaki
nonlinear response relation. Furthermore, by using a non-equilibrium identity similar to the fluctuation theorems
and assuming a local Gibbs distribution at the initial time, the Navier–Stokes equation was derived for an isolated
Hamiltonian system [1]. Based on these achievements, we believe this is an opportune moment to reconsider fluid
dynamics from the viewpoint of statistical mechanics.
In this presentation, we study the friction coefficient of a macroscopic sphere in a viscous fluid at low Reynolds
number from the viewpoint of statistical mechanics. First, according to Kirkwood’s formula [2], the friction
coefficient is expressed in terms of the stress correlation on the surface of the macroscopic sphere. The stresscorrelation in the bulk of the fluid is characterized by the viscosity in the Green–Kubo formula [3]. Then, weestablish the connection between the bulk and surface stress fluctuations. The basic concept is simple. The
probability density of surface stress fluctuations is obtained from the probability density of bulk stress fluctuations
by integrating out the other degrees of freedom. This procedure can be conducted in an elegant manner with theaid of large deviation theory. Finally, by combining Kirkwood’s formula and the Green–Kubo formula in large
deviation theory, we derive Stokes’ law [4] without explicitly employing the hydrodynamic equations [5].

References[1] S. Sasa, Phys. Rev. Lett. 112, 100602 (2014).
[2] J. Kirkwood, J. Chem. Phys. 14, 180-201 (1946).
[3] M.S. Green, J. Chem. Phys. 22, 398-413 (1954).
[4] G.G. Stokes, Trans. Cambridge Philos. Soc. 9, 8-106 (1851).
[5] M. Itami and S. Sasa, J. Stat. Phys. 161, 532-552 (2015).

Shape fluctuation and deformation of biological soft interfaces
Dissipative structure and Biological physics laboratory

Hiroaki Ito

Abstract To understand the complex behaviors of cell membranes as non-equilibrium interfacial
phenomena, we experimentally investigated the shape fluctuation and deformation of biological softinterfaces, consisting of lipid membrane and underlying cytoskeletal structure, using living andnon-living systems, especially through the aspect of the interplay between them.
© 2016 Department of Physics, Kyoto University

Cell membrane is a soft interface consisting of a phospholipid fluid bilayer in which large amount of membraneproteins are embedded. The membrane is further connected to underlying cytoskeletal network structure, andcarries out a number of biological processes under the fluctuation and flexible deformation. In our recent works,
we have experimentally investigated the characteristic interfacial phenomena of biological matters to understandthe fundamental properties of cell membrane fluctuation and deformation. For example, we focused on the shapefluctuation of a red blood cell as the simplest membrane/cytoskeleton system. By combining a microfluidic
technique and the wavenumber analysis of the shape fluctuation, called flicker spectroscopy, we directlycompared the fluctuations before and after the influence of toxic agent, lipopolysaccharides, and confirmed theclear increasing effect on the attractive interaction between the cell membrane and cytoskeleton[1].
In contrast to the above passive fluctuation, in living organisms, active membrane deformation plays crucial
roles in various biological processes, such as cell motility, cell division, embryonic development, etc. These
dynamic membrane deformations are mainly caused by the active force generation by actomyosin, which is a
protein complex of actin filaments and type II myosin. For the better understanding of the native properties ofactomyosin, bottom-up/reconstituted systems have been adopted using only a small number of components
involved in the force generation so far[2]. These studies have successfully verified the active contractile propertyof purified actomyosin and its higher order structure formation. To reveal the fundamental contribution of thisactive force generation to a deformable soft interface, we have developed a reconstituted experimental system,
namely cell-sized water-in-oil droplets with lipid layers connected to actin and myosin by electrostatic attraction.
As a result, we successfully reconstituted the active membrane fluctuation and deformation driven by actomyosin
in vitro for the first time; we observed (i) non-periodic oscillatory undulation and (ii) curvature-dependent
dynamic deformation of the interface induced by the contractile force of actomyosin hierarchical structures(Fig.1)[3].
	
 
	
 
	
 
	
 
	
 
	
 
	
 
	
 
	
 
	
 
Fig. 1. (a) Reconstituted system. (b) (i) active fluctuation and (ii) dynamic deformation	 induced by actomyosin in a reconstituted system.
	 References[1] H. Ito et al., J. Phys. Chem. B 119, 7837-7845 (2015).
[2] K. Takiguchi et al., Langmuir 27, 11528-11535 (2011).; K. Carvalho et al., PNAS 110, 16456-16461 (2013).
[3] H. Ito et al., arXiv:1505.04371v2 (2015).

Nonlinear analysis of the interfacial layer effects on the surface
capacitances and electro-osmosis in electrolyte solutions
Phase Transition Dynamics Group	  	  Yuki Uematsu
Abstract We investigate the structure of electric double layer with effects of Stern layer. We construct anapproximation for a modified Gouy-Chapman model with inhomogeneous dielectric constant andviscosity. Nonlinear analysis reproduces the numerical solution of the original equation. Also, the surface
capacitance and the electro-osmotic mobility are calculated. © 2016 Department of Physics, Kyoto University	  Electro-osmosis is the motion of electrolyte solutions induced by electric field across a capillary tube. It plays
important roles in many systems such as industry and bio-systems. A well-known model describing theelectro-osmosis is based on Poisson-Boltzmann and hydrodynamic equations. They describe electric diffuse
double layers near a charged flat surface. However, this model cannot reproduce some experimental observations
such as the surface capacitances and the saturation of electrokinetic surface charge correctly. Then a modified
Poisson-Boltzmann equation considering the interfacial (Stern) layer effect was proposed [1]. It is given by$" εκ 2 sinh Ψ for 0 < z < z*
=#
2
2
*
dz
$% κ sinh Ψ for z < z
2

d Ψ

(1)

*

where Ψ = eψ / kBT is the dimensionless electrostatic potential, z = 0.1 nm is the thickness of the interfacial−1layer, ε =80.4 is the dielectric constant of water, and κ is the Debye length. The temperature T is set to 300 K.
However, eq. (1) is still difficult to solve analytically because its general solution contains elliptic functions. Then,
we approximate eq. (1) by neglecting the existence of co-ion in the interfacial layer [2]. Assuming that the surface
is negatively charged and the co-ion is cation, eq. (1) is rewritten to# εκ 2−Ψ*% −e
for 0 < z < z
=
$
2
2
dz
% κ 2 sinh Ψ for z* < z
&
2

d Ψ

(2)

This approximation is reasonable for the surface with −Ψ << 1 in the interfacial layer. We obtained theanalytical solution of eq. (2) and discussed whether the approximation is valid or not by comparing the numericalresults of eq. (1) and the analytical solution of eq. (2). Fig.1 shows the comparisons for various quantities. Clearly,
this approximation works well when the surface potential is negative and the salt concentration is sufficiently low.
0.35

-0.1
-0.01

1

0

-1

-σek [e/nm2]

0.01

0

0.3

101
100mM

0.05

100mM
Eq.(1)
1mM
Eq.(1)

0.1
10

eq.(1)

0.25
C [µFcm-2]

σ0 [e/nm2]

102

0

-0.05

PB

5

0
Ψ0

0.2

hydrophobic 100mM

0.15
0.1

Eq. (1)hydrophilic 100mM

0.05
100

-5

-10

0

0

20 40 60 80 100 120 140-ψ0 [mV]

0 0.05 0.1 0.15 0.2 0.25 0.3 0.35
-σ0 [e/nm2]

Fig. 1. (Left) Surface charge density as functions of the surface potential. (Center) Surface capacitance as functions of
the surface potential. (Right) Electrokinetic surface charge density as functions of the bare surface charge density.

References[1] D. J. Bonthuis and R. R. Netz, Langmuir 28, 16049 (2012).
[2] Y. Uematsu, D. J. Bonthuis, and R. R. Netz, in preparation.

Disorder effects on quantum phase transitionof 4He in nanoporous media
Condensed matter theory group

Yu Ogata

Abstract We theoretically investigate disorder effects on the quantum phase transition of 4He in
nanoporous media. We show that the randomness of media extends the superfluid region to lowtemperature and high pressure area, leading to the existence of the Bose glass phase at higher pressure.
© 2016 Department of Physics, Kyoto University

Recently, 4He confined in nanoporous media which has a 3D random network structure of a few nm pores has
attracted much attention. The superfluid transition temperature Tc is drastically suppressed with increasingpressure and approaches 0 K at a critical pressure Pc [1]. Moreover, it is revealed that there exists a localized BEC(LBEC) state where BEC “islands” are grown in broader pores at higher temperatures and pressures than the
superfluid phase boundary [2, 3]. The LBEC intervenes between the normal and the superfluid phases.
The suppression of Tc is theoretically explained by the Josephson junction array model with no randomness.
However, the deviation from the experimental data still exists near the apparent quantum critical point (QCP). It
would originate from the disorder effect.
In order to clarify the behavior near the QCP, we investigate disorder effects on the system. We introduce therandomness into the Josephson coupling term connecting between LBEC islands. The obtained phase diagram isshown in Fig. 1. First, the superfluid region is highly extended to low temperature and high pressure area. Second,
the Bose glass phase, which is characteristic of the system with randomness, appears at higher pressure. We
explain the deviation which has not been explained in a previous study [4], and propose the nature of quantum
phase transition in this system.
12.3
12.2

TBG

U/J0

12.1

TMF

12

Tc
11.9
11.8
11.7

Superfluid
0

0.05

0.1

0.15

0.2

0.25

0.3

T/J0
Fig. 1. Pressure-temperature phase diagram.

References[1] K. Yamamoto, H. Nakashima, Y. Shibayama, and K. Shirahama, Phys. Rev. Lett. 93, 075302 (2004).
[2] K. Yamamoto, Y. Shibayama, and K. Shirahama, Phys. Rev. Lett. 100, 195301 (2008).
[3] J. Bossy, J. V. Pearce, H. Schober, and H. R. Glyde, Phys. Rev. B 78, 224507 (2008).
[4] T. Eggel, M. Oshikawa, and K. Shirahama, Phys. Rev. B 84, 020515(R) (2011).

Mode bifurcation of a chiral asymmetric dumbbell on a verticallyvibrated plate
Dissipative structure and Biological physics laboratory Yoshitsugu KUBO
Abstract We studied the behavior of a chiral asymmetric dumbbell bouncing upon a sinusoidally
vibrating plate. We observed a cascade of bifurcations with an increase in the vibration amplitude:
spinning, orbital, and rolling. The mode bifurcation from directional motion to random motion isinterpreted analytically by a simple mechanics.
© 2016 Department of Physics, Kyoto University

Spatiotemporal self-organization under nonequilibrium is one of intriguing research topics in modern
physics. Sometimes a simple system involves rich nonlinear behaviors under nonequilibrium conditions. For
example, just a bouncing object has attracted considerable interest, where various bifurcations, including theappearance of chaos, have been reported [1-3]. It has been shown that an axisymmetric dimer moves either
forward or backward, depending on the initial conditions [1]. In this study, we demonstrate how the breaking ofchiral symmetry creates a new scenario in the mode bifurcation of a bouncing dumbbell on a vibrating plate.
Two-dimensional motions on the horizontally set plate, such as orbital and spin motions, were observed eventhough the plate was applied only vertical agitation isotopically.
In the experiment, cascade of different modes on two-dimensional motions were observed by introducing
chiral asymmetry into a dumbbell particle under vertical vibration. By increasing vibration strength of the plate,spinning motion accompanied by random behavior of the centroid, now denoted SR mode, and spinning motion
accompanied by directional motion (O mode) were emerged after translationally random motion. In addition, theSR and the O modes switched in a subcritical manner as a function of Γ, which is a normalized order parameter
describing vibration strength. It was also shown that the angular velocity of the spinning motion that originatesin the chirality is determined by sin(β’/2). A simple mechanicalmodel was considered to obtain the lower limit of Γ for the
directional motion of the dumbbell. Figure 1 shows that theestimated critical acceleration Γc agreed well with the experimental
results and with simulation results which reproduces bifurcation
between SR and O modes. The condition for periodic collision of
the upper sphere appeared to have functional form identical to thatof a single bouncing ball.
.

FIG..1. Dependence of the critical[1] S. Dorbolo, D. Volfson, L. Tsimring, and A. Kudrolli,
Dynamics of a Bouncing Dimer, Phys. Rev. Lett. 95,
044101 (2005).
[2] D. Yamada, T. Hondou, and M. Sano, Coherent
dynamics of an asymmetric particle in a verticallyvibrating bed, Phys. Rev. E 67, 040301 (2003).
[3] J. Wang, C. Liu, Y.-B. Jia, and D. Ma, Ratchet rotationof a 3D dimer on a vibrating plate, Eur. Phys. J. E 37, 1(2014).

acceleration Γc on the restitution
coefficient e.’ Lower limit of steadycollision in the theoretical analysis(dotted line), experiments (green
square), and numerical simulation withβ’ = 0.01π (blue triangles), β’ = 0.75π(red circles), and ρ1 = ρ2 (cyandiamonds). Experimental data are given
for rubber (e’ = 0.223 ± 0.024),
aluminum (e’ = 0.305 ± 0.008), andglass plates (e’ = 0.472 ± 0.026).

Coherence resonance occurred in oscillatory motion ofa micrometer-sized droplet between electrode needles
Dissipative structure and Biological Physics GroupTomo Kurimura

Abstract We have discovered the oscillating water droplet in an oil phase between the cone-shaped
electrodes as a limit cycle. We found the noise can make the system oscillate when the voltage wasslightly lower than the threshold. The result shows the new way to design an efficient nanometer-sizedmachine. © 2016 Department of Physics, Kyoto University

Position of droplet (µm)

The small world is sticky and noisy. Viscosity is dominant in comparison with the inertia at the micrometerscale. Thermal fluctuation becomes significant in the motions of micro- to nano-objects. The conditions underwhich the micro- and nano-machines will be working require continuous force for continuous motion andresistibility against thermal noise. When we make such a machine in the conventional engineering way, it would
be hard to reproduce the desired motion, as we are doing. For this reason, we have to find an innovative way toconstruct a nano- or micro-machine. One way to overcome this difficulty is to use or study the mechanism of
biological motor proteins, which already exist in organisms [1]. The features of the mechanism will be utilized
in the driving forces of the surrounding noisy environment. In our study, we used the micro-sized oscillation thatis robust for perturbation, the limit cycle oscillation, and demonstrated that the system can generate a regularmotion despite adding noisy external force.
At first, we briefly introduce a limit cycle oscillation. The difference of the limit cycle for a normal oscillation
in a conservative system is a stable orbital. The track of the limit cycle is attractive and independent of the initialvalue. When one of the parameters substituting for an order parameter was increased or decreased, the systemchanged from oscillatory to stationary by crossing a bifurcation point. Below this threshold, the system would
take an excitable state. In the excitable state, the system does not oscillate autonomously but shows asymptotic
oscillation for one period stimulated by external force. Numerical simulations have shown that adding noisy
external forces induces an excitable state of the pseudo limit cycle oscillation. This oscillatory behavior is called
coherence resonance. We discovered an oscillation of a water droplet in an oil phase between cone-shaped
electrodes and confirmed this oscillation as a limit cycle. Charging and discharging of the droplet at theelectrodes, and electric and dielectric forces(a) 35.8 V + 41.8 V p-p
cause this cycle. We also observed that thesystem reaches an excitable state near thethreshold voltage. We here tried to generate
0
0
10
20
30
40
an oscillation on the system below the(b) 35.8 V + 23.7 V p-p
100
threshold by adding noisy external
perturbation. Noise application successfullycaused the system to oscillate even when the
0
0
10
20
30
40
voltage is slightly lower than the threshold.
(c) 35.8 V + 5.8 V p-p
100
The oscillation strength resonates with themagnitude of noise (Fig. 1).
0This phenomenon indicates a novel
0
10
20
30
40
t (s)
approach for nano-machines in whichrhythmically ordered motion can be stabilized
Fig. 1 Time Evolution of the droplet position. The voltage fromby the utilization of a noisy external force.
the amplifier is (a) 35.8 V + 41.8 Vp−p, (b) 35.8 V + 23.7
References
Vp−p, (c) 35.8 V + 5.8 Vp−p. The position of the droplet was[1] M. G. L. van den Heuvel, Science, 317
measured along the line between the electrodes. The position of
333(2007)
electrodes is about 100 and 20 μ m (the dashed lines).

An ultracold Fermi gas with localized impurities in an opticallattice with controllable interaction
Quantum Optics Group

Hideki Konishi

Abstract Lifetimes of the metastable 3P2 state of ytterbium (Yb) in the presence of the 2S1/2 ground stateof lithium (Li) in an optical lattice were measured. A fast decay due to inelastic collision between Yb andLi was observed. A search for Yb(3P2)-Li(2S1/2) Feshbach resonances is now underway.
© 2016 Department of Physics, Kyoto University

Over the last two decades ultracold atoms have proven to be a valuable system to investigate quantum
many-body physics. We can explore wide range of research fields thanks to useful tools such as optical lattices,
defect-free periodic potential made by standing wave of light, and Feshbach resonances, controlling of interatomic
interactions by magnetic field. Applying these techniques on an ultracold atomic mixture composed of amass-imbalanced atomic pair, one can design a system of atoms subject to different dimensions [1].
An ultracold mixture of ytterbium (Yb) and lithium (Li), which has an extreme mass imbalance of about 29,
is one of the promising systems to study physics in mixed dimensions. Loaded in an optical lattice, Yb atoms are
deeply localized in lattice sites while Li atoms are itinerant over a whole system, which realizes a mixture of Yb
atoms confined in low dimensions and a three-dimensional Li atomic gas. As for the inter-species interaction,
unlike well-used alkali atom pairs, there are no usable Feshbach resonances between the ground states of Yb andLi. However, the metastable excited 3P2 state of Yb offers an interesting possibility to tune interaction between
Yb(3P2) and Li by means of Feshbach resonances. In fact, Feshbach resonances between Yb in the 3P2 state and Li
in the ground state are discussed both in theory and experiment. [2, 3, 4].
As a first step, we developed a method to compensate gravitational sag between Yb and Li to obtain a spatial
overlap of two atom clouds. Combining this method with an ultra-narrow optical transition of 1S0-3P2 for impurity
atoms of Yb, we could successfully observe the collisional instability of 174Yb(3P2) induced by Li(2S1/2). A typicalresult at 3 Gauss is shown in Fig. 1. A faster decay was observed in the case with Li. The fast decay time constant
was determined to be about 20 ms while the slow decay was about 1000 ms. Here we note that, by exciting
singly-occupying Yb atoms in a Mott-insulator state in an optical lattice, the results get insensitive to unwanted
Yb(3P2)-Yb(3P2) and Yb(3P2)-Yb(1S0) collisional channels. In this way, we could demonstrate the modification of
the inelastic collision property between the
Fermi gas of Li and the impurity atoms of Yb
localized in an optical lattice.
To find usable 174Yb(3P2)-Li Feshbachresonances, we are now repeating the decay
measurement of the 174Yb(3P2) in the presence of
Li for various magnetic fields. Also we try
fermionic 173Yb that is expected to be morefavorable to induce Feshbach resonances,174
3
because it has many hyperfine structures, which Fig. 1. Observed decay of the P2 (mJ = 0) state of Yb
atoms in an optical lattice with Li (filled red circle) andallow many channels to couple.
without Li (open blue square) at 3.0 G of magnetic field.
Lines are fits to the data.
References[1] Y. Nishida, Phys. Rev. A 82, 011605.
[2] A. Petrov et al., New J. Phys. 17, 045010 (2015).
[3] T. Chen et al., New J. Phys. 17, 103036 (2015).
[4] W. Dowd et al., New J. Phys. 17, 055007 (2015).

Emergent quantum phenomena
in inhomogeneous optical lattices
Condensed matter theory group

Masaru Sakaida

Abstract We investigate the attractively interacting Fermi systems with spatial nonuniformity. A
statistical dynamical mean-field theory and a Bogoliubov-de Gennes method are extended to analyze thesystems considered here. Employing these methods, we elucidate how disorder and interaction
compete/cooperate with each other. Also, the disorder-triggered transitions in multicomponent systems
are uncovered.
© 2016 Department of Physics, Kyoto University

Thanks to high controllability, optical lattices with spatial nonuniformity have been successfully realized. One of
the notable advantages of these systems is that we can investigate the effects of nonuniformity even in strongly
disordered regions[1], whereas it is difficult to experimentally address such regions in solid physics. Disorderedsystems have been already studied for more than five decades[2], but there are still many open questions. The
optical lattices with spatial disorder are expected to give a new insight into these remaining questions, and thus it
is an urgent issue to develop the theory for such lattices.
It is another advantage of cold atoms that we can realize the novel systems such as Bose-Fermi mixed systems,
multicomponent Fermi systems, and so on. Especially, the recent realization of the quantum degenerate states ofatoms with many hyperfine states[3] attracts our attention to multicomponent Fermi systems. Although themulticomponent Fermi systems have also been analyzed for a long period, rich phases and nontrivial properties
due to many degrees of freedom are not fully clarified yet. Namely, what kind of state is stabilized as a groundstate in multicomponent Fermi systems with spatial nonuniformity is an important one of left issues.
Motivated by these backgrounds, we study N-component Fermi systems with spatial in-homogeneity using astatistical dynamical mean-field theory to address the N=2 case and a Bogoliubov-de Gennes method to the N=3
and 4 cases. The distribution functions of the local density of states and the s-wave superfluid order parameter are
obtained in N=2. From the geometrical averages estimated from these distribution functions, the ground-statephase diagram of the 2-component Anderson-Hubbard model with the attractive correlation at zero temperatureand half-filling is determined. In the N=3 and 4 cases, the charge correlation function, the singlet pairing
amplitude, and the free energy of each phase are calculated. In this study, we uncover that spatial disorder induces
the phase transition from a density-wave phase to a superfluid phase in 3-component systems. It is also clarified
that a further increase of the disorder strength destroys the long-range order of the superfuluid state and thus thesuperfluid state undergoes a transition to the Anderson localized state. We conclude from the calculations of thefree energy of each state that these disorder-driven transitions are of first order. From the similar calculations
performed for N=4, it is demonstrated that the density-wave state directly undergoes a transition to the Anderson
localized state; there are no regions where the superfluid state is stabilized as a ground-state in 4-component
systems. This observation leads us to claim that for N >3 the density-wave state may undergo a direct transition to
the Anderson localized state without stabilizing the superfluid state in between. Also, comparing the ground-statephase diagrams of the N=3 and 4 cases determined in this research, we clarify that the density-wave state in N=4
is more robust than that in N=3. This result implies that with an increase of N the density-wave state gradually
becomes robust over spatial nonuniformity and possibly other perturbations such as thermal fluctuations.
References[1] J. Billy et al., Nature 453, 891-894 (2008).
[2] P. W. Anderson, Phys. Rev. 109, 1492-1505 (1958).
[3] B. DeMarco et al., Science 285, 1703-1706 (1999), A. G. Truscott et al., Science 291, 2570-2572 (2001),
T. Fukuhara et al., Phys. Rev. Lett. 98, 030401 (2007), B. J. DeSalvo et al., Phys. Rev. Lett. 105, 030402 (2010)

Studies on Non-equilibrium Fluctuating Motion
as a Rectiﬁer
Advanced Statistical Dynamics GroupTomohiko Sano

Abstract Fluctuating motion of piston under nonlinear friction is studied as a rectifier of momentum flux.
We study the motion of an adiabatic piston under the mechanical equilibrium, which is located between
two equilibrium environments characterized by two different temperatures and densities. We show thatthe direction of momentum flux rectified from the fluctuation piston is not determined by temperature
difference, if the piston is attached to non-equilibrium environments.
© 2016 Department of Physics, Kyoto University

Extraction of work from systems attached to thermal equilibrium environments is an important topic inthermodynamics and statistical mechanics. The milestone of equilibrium thermodynamics is the Carnot efficiency,
which is realized in quasi-static operation and is the maximum efficiency [1]. For practical point of view, theCarnot efficiency is useless, because work per a unit time (power) is zero. Extension of equilibrium
thermodynamics toward finite time operation, i.e. finite time thermodynamics, where one can ask the efficiency at
maximum power output, has been one of the important topic in non-equilibrium statistical mechanics. Whether
the operation is finite time manner or not, we partition the system (gas) in the container by a piston, when we
discuss the efficiency or power of the engine. We usually assume that the piston is attached to thermal gases only,
and is operated in completely deterministic manner, although the piston itself can be far from thermal equilibrium.
Therefore, it is important to consider the extraction of work, when the piston is attached to non-equilibrium
environment, or is subjected to non-equilibrium fluctuation.
One of the ubiquitous non-equilibrium environments is friction, which can be regarded as the zerotemperature environment [2]. For practical point of view, controlling a small fluctuating object under friction isimportant, such as the application to nano-motors under axial friction. Experiments for macroscopic systems
under dry friction reveal that the dry friction has an important role to rectify unbiased fluctuations, i.e., to extract
work from an equilibrium environment. Although dry friction plays essential roles in non-equilibrium transport
and it is ubiquitous throughout nature from a biological surface to an atomic-scale surface, the energetics for thesystems under dry friction has been elusive so far. In this talk, we study energy transfer, such as momentum orheat transfer, for systems with a fluctuating boundary under nonlinear friction. For this purpose, we study the
one-dimensional motion of an adiabatic piston under the mechanical equilibrium, which is located between two
equilibrium environments characterized by two different temperatures and densities. Lieb suggested that theequilibrium thermodynamics cannot tell us whether the adiabatic piston moves or not [3]. This problem is solved
analytically by using the Boltzmann-Lorentz equation and is recently phenomenologically understood through theconcept of the momentum transfer deficit due to dissipation (MDD) [4]. However, the motion of the adiabatic
piston under sliding friction is little known [5].
In the absence of sliding friction, the direction of the piston motion is known to be determined from thedifference of temperature of two gases only. However, if sliding friction exists, we show that the direction of
motion depends on the amplitude of the friction, and nonlinearity of the friction, i.e. the direction of momentum
flux rectified from the fluctuation piston is not determined by temperature difference, if the piston is attached to
non-equilibrium environments.

References[1] H. Callen, Thermodynamics and an Introduction to Thermostatistics, 2nd edition (Wiley, New York, 1985).
[2] B. N. J. Persson, Sliding Friction (Springer-Verlag, Berlin, 2000).
[3] E. H. Lieb, Physica A 263, 491 (1999).
[4] Ch. Gruber and J. Piasecki, Physica A 268, 412 (1999), A. Fruleux, R. Kawai, and K. Sekimoto, Phys. Rev.
Lett. 108, 160601 (2012).
[5] T. G. Sano and H. Hayakawa, Phys. Rev. E 89, 032104 (2014).

Transition dynamics from macro- to micro-phase separationin asymmetric lipid bilayers
Dissipative Structure and Biological Physics

Shunsuke Shimobayashi

Abstract We reveal transition dynamics from macro- to micro-phase separation in multicomponent
asymmetric lipid vesicles exposed to externally added glycolipids. Numerical analysis gives us insights
into the mechanism of the novel transitions, which is apparently governed by the local spontaneous
curvature induced by the local asymmetric lipid composition.
© 2016 Department of Physics, Kyoto University

In general, phase separation in binary liquid mixtures completes by relaxation below the transition temperature.
The coarsening dynamics to complete phase separation have been extensively investigated in binary mixture
systems of polymeric and/or low molecular weight molecules. In contrast, the reverse dynamics from macro- tomicro-phase separation remains poorly understood because no appropriate experiments and models exist forinvestigating this phenomenon.
Phase separation in reconstituted lipid membranes has become intensively researched, because it might explain
the nanosized heterogeneities observed in cell plasma membranes. However, micrometer-sized domains arereadily reconstituted in giant unilamellar vesicles (GUVs) formed from lipid mixtures. Eventually, these domains
are thought to coalescence into a single domain. However, recently it has been suggested that molecular dopingwith proteins or head-bulky lipids can modulate the stable morphologies of phase separation, enhancing thestability of micro-phase separation [1]. However, the transition dynamics from macro- to micro-phase separation
by added guest molecules is still veiled.
In this talk, we present the direct observations of morphological transitions from macro- to micro-phaseseparation using micrometer-sized asymmetric lipid vesicles exposed to externally added glycolipids (GM1)(Figure 1(a)-(c)). The transition occurs via stripe morphology as a metastable state. During the transition,
monodisperse micro domains emerge through repeated scission events of the stripe domains (Figure 1(c)).
Moreover, we numerically confirmed the transitions by the time-dependent Ginzburg-Landau model, which
describes phase separation and bending elastic membrane (Figure 1(d)). Numerical results suggest the crucial roleof the local spontaneous curvature induced by the local asymmetric lipid composition.

Fig. 1. (a) Top-view images of giant unilamellar vesicles with three distinct morphologies through confocal
fluorescent microscopy. (b,c) Sequential top-view images of each vesicle transiting from macro- to stripe-phase andfrom stripe- to micro-phase, respectively. (d) Transition dynamics from macro- to micro-phase separation in the 3D
numerical analysis. Green and red regions represent two different phases, respectively. Scale bars are 5 µm.

References[1] C. S. Scheve, P. A. Gonzales, N. Momin, and J. Stachowiak, JACS 135 1185 (2013).
[2] S. F. Shimobayashi, M. Ichikawa, and T. Taniguchi, submitted (arXiv: 1504.03038).

Density-matrix renormalization group study of quantum
spin systems with Kitaev-type anisotropic interaction
Physics of Matter: Condensed Matter Physics (YITP)

Kazuya Shinjo

Abstract We study an extended Kitaev-Heisenberg model including anisotropic off-diagonal couplings
by using two-dimensional density-matrix renormalization group method. Calculating the ground-stateenergy and spin-spin correlation functions, we make a phase diagram of the model. The entanglement
properties of the Kitaev spin-liquid phase in the phase diagram are discussed.
© 2016 Department of Physics, Kyoto University	 	  Since it has been found that the ground state of the Kitaev model on honeycomb lattice provides
exactly-solvable examples of spin liquids [1], candidate materials for the model have been investigated. One of
the candidates is Na2IrO3 in which spin-orbit coupling of Ir plays an important role. Na2IrO3 consists ofwell-separated honeycomb layers, and the Kitaev-Heisenberg model with the Kitaev-type anisotropic exchangeinteraction coming from strong spin-orbit coupling as well as the usual Heisenberg interaction between Ir ions has
been proposed as an effective spin model [2]. However, it has turned out that the model cannot naturally explain
zigzag antiferromagnetic order observed in experiments of Na2IrO3 [3]. Therefore, further investigation ofaugmented effective models for Na2IrO3 taking into account anisotropic off-diagonal interactions coming fromtrigonal distortion attracts much attention.
We first consider an extended Kitaev-Heisenberg model including additional anisotropic off-diagonal
couplings (model-1) by using two-dimensional density-matrix renormalization group (DMRG) method [4].
Calculating the ground-state energy, the entanglement entropy, and the spin-spin correlation functions, we makethe phase diagram of the extended Kitaev-Heisenberg model around the spin-liquid phase. We found a zigzag
antiferromagnetic phase, a ferromagnetic phase, a 120-degree antiferromagnetic phase, and two kinds ofincommensurate phases around the Kitaev spin-liquid phase. We have checked that the zigzag antiferromagnetic
phase is continuously connected to the ground state of a more realistic Kitaev-Heisenberg model (model-2)
derived by ab initio study of Na2IrO3 [5]. Furthermore, we also investigated the model-2 by DMRG and foundzigzag antiferromagnetic phases, a 120-degree antiferromagnetic phase, a 16-sites unit cell phase, and an
incommensurate phase with changing trigonal distortion.
Finally, we study the entanglement entropy and the entanglement spectrum of the extended Kitaev-Heisenberg
model (model-1). These quantities can detect non-local correlation inherent in topologically-ordered states andhave recently been introduced to condensed matter physics from quantum informational physics to characterize
topological order in fractional quantum Hall states and quantum spin liquids [6]. Then, we found that theentanglement levels in the Kitaev spin-liquid phase are degenerate forming pairs while those in the magneticallyordered phases are non-degenerate. The number of degeneracy depends both on the size of the boundary of thesubsystem and on the boundary condition. The Schmidt gap defined by the difference between the two lowest
entanglement levels changes at the phase boundaries of the Kitaev spin-liquid phase, although it is not necessarily
useful in characterizing phase transitions between magnetically ordered phases.
References[1] A. Kitaev, Ann. Phys. (NY) 321, 2 (2006).
[2] J. Chaloupka et al., Phys. Rev. Lett. 105, 027204 (2010).
[3] S. K. Choi et al., Phys. Rev. Lett. 108, 127204 (2012); F. Ye, et al., Phys. Rev. B 85, 180403 (2012).
[4] K. Shinjo et al., Phys. Rev. B 91, 054401 (2015).
[5] Y. Yamaji et al., Phys. Rev. Lett. 113, 107201 (2014).
[6] A. Kitaev and J. Preskill, Phys. Rev. Lett. 96, 110404 (2006); M. Levin and X.-G. Wen, Phys. Rev. Lett. 96,
110405 (2006).

Estimating effective connectivity between brain areas
with DCM
Nonlinear Dynamics Group

Toshiaki Shintani

Abstract Recent advance of fMRI techniques enables us to analyze the connectivity of entire brain. DCM
is the estimation method for the connectivity but it is generally difficult to infer a number of connections
among many brain areas. We proposed a solution strategy and validated the method.
© 2016 Department of Physics, Kyoto University

When our brain processes the external information, the blood flow volume in the regions relatedwith the process changes, and the blood oxygen level changes because of the consumption of oxygen
for the activity of neurons. Using this fact, functional magnetic resonance imaging (fMRI)
techniques image the brain activity from the change of the blood oxygen level.
The recent advance of fMRI enables the research for the correlation of the brain activity. The
networks of the influence of the activity of a brain area over that of another area is called
effective connectivity, and the analysis of the connectivity from fMRI data is important forunderstanding the information processing in the brain. The dynamic causal modeling (DCM) [1]is an estimation method which can analyze the changes in the effective connectivity across thebrain areas.
It is well known that fMRI data has many causes of the noise. In the study with DCM, the observationnoise is assumed, and it is expected that the original signal fluctuations cannot be detected
if the observation noise is large [2]. To examine the manner in which the signals are obscured,
we create the data with the connectivity model presented in the previous study [1] and examine
the parameter region where one can recover the model from the data for various signal-to-noise
ratios (SNRs).
In DCM, we create various connectivity models of the interested brain areas and select the model
which can most likely explain the fMRI data. However, the model selection process is difficult
to calculate when the number of areas increases. In the present study, we adopted a method of
automatically pruning connections based on individual levels of confidence given the data, which
does not require arbitrary operations. We estimated with the method for various prior variancesof the connections and found the optimal parameter region of the prior variance and the SNRs
where one can recover the model.

References[1] K. J. Friston, L. Harrison, and W. Penny. Dynamic causal modelling. NeuroImage, 19(4):1273–1302, 2003.
[2] T. Shintani and S. Shinomoto. Detection limit for rate fluctuations in inhomogeneous Poisson processes. Phys.
Rev. E, 85, 041139, Apr 2012.

Kinetic theory for cohesive granular gaseswith a square well potential
Advanced Statistical Dynamics Group

Satoshi Takada

Abstract We study the kinetic theory of dilute cohesive granular gases whose attractive part is describedby a square well potential. We derive a set of hydrodynamic equations from the kinetic theory with thedissipation rate and the transport coefficients. We also perform the numerical simulations to check thevalidity of our theory.
© 2016 Department of Physics, Kyoto University

Because granular materials are ubiquitous in our daily lives, to understand their properties
is important in both physics and industry. Granular materials behave as unusual solids, liquids,
and gases. Even though we consider the most idealistic case, a system for a dilute gas without
any external force, the system cannot maintain a homogenous state due to inelastic collisions
between grains. Such inhomogeneity can be understood by the instability of granularhydrodynamics.
Although the interaction between idealistic granular materials are assumed to be repulsive
short range force, cohesive force cannot be ignored for fine powders or wet granular system.
In a previous study [1], we have shown the appearance of various phases for cohesive powders
under a plane shear. We have also demonstrated that the dynamic van der Waals model under a plane
shear can reproduce such phases and clarified the mechanism of the instability which is mainly
caused by the cohesive force for small systems [2].
In this study, we extend the kinetic theory of the inelastic hard core system to the nearly
elastic granular gases whose attractive part is given by a square well potential. We derive aset of hydrodynamic equations using theChapman-Enskog theory and obtain thedissipation
rate
and
the
transport
coefficients of this system [3]. Our
theoretical viscosity is consistent with theprevious results for elastic gases [4] (Fig.
1). We find that the transport coefficientsare identical to those for hard core system of
the diameterin the high (low)temperature limit ( is the well width ratio).
We also try to examine various numericalmethods such as the discrete Monte Carlosimulation
andevent-driven
molecular Fig. 1. The granular temperature dependence ofdynamics simulation to verify the validity of the shear viscosity obtained by the kinetic
the kinetic theory.
theory and that by the DSMC.
References[1] S. Takada, K. Saitoh, and H. Hayakawa, Phys. Rev. E 90, 062207 (2014).
[2] K. Saitoh, S. Takada, and H. Hayakawa, Soft Matter, 11, 6371 (2015).
[3] S. Takada, K. Saitoh, and H. Hayakawa, arXiv:1506.04578.
[4] E. M. Holleran and H. M. Hulburt, J. Chem. Phys. 19, 232 (1951).

Ejection-Jet cycle: self-sustaining mechanism of
turbulent-laminar interface
Fluid Physics Group

Toshiki Teramura

Abstract A self-sustaining interface structure between turbulence and laminar flows is investigated in two-dimensional channel flow. A simple description for the multi-scale interaction between vortex ejections on the both walls (small scale) and a meandering jet (largec 2015 Department of Physics, Kyoto University
scale) is introduced.
Sustaining mechanism of nonlinear structures in turbulent flows is one of central issues of recent
turbulence studies, which is mainly motivated by “self-sustaining process” (SSP) in minimal plane
Couette flow. Different from classical techniques in vortex dynamics, i.e. idealized vortex modeling,these authors used exact, fully-resolved simulations of Navier-Stokes equation without any approximations. We try to extend their techniques to more general flows, e.g. turbulent-laminar interfaces.
We set Reynolds numPeriodic BC
ber Re = 8000 > Rec to
Laminar flow
make the laminar PoiseuilleΩ
Patternflow unstable. Then the turInterface does not marchbulent region becomes wider
damping regionx 0 = x + cI t
by invading the laminar region. We focus on the interFig. 1: Setting for the filtered simulation.
face dynamics between turbulent and laminar regions. This interface eventually disappears in a finite computational region
since the laminar region turns to turbulence. We utilize filtered simulation technique [1] to keep theinterface permanently:(
1 (x0 ∈ Ω)
∂u
1 2
0
0
+ (u · ∇) u = −∇p +∇ u − HΩ (x ) (u − UL ),HΩ (x ) ≈.
∂tRe
0 (otherwise),
Since the interface invades at a constant speed cI , we consider the inertial frame x0 where the interface
does not march. On this interface frame, we damp turbulence into laminar on a narrow spatial regionΩ. This setting approximately corresponds to an infinitely long channel flow setting.
To understand the origin of cI , we investigate
the dynamics of the interface structure. First, we(iv)
find the interface is self-sustainable; if we damp
Jet
the turbulent region using the filtered simula(iii)tion, the interface keeps alive. In addition, the(i)(ii)
vortex dynamics in the interface is temporally Ejection
chaotic. So this interface is a self-sustaining coherent structure, and we call it “chaotic inter- Fig. 2: A schematic figure of Ejection-Jet cycle
face” (CI). The self-sustaining mechanism of CI (quoted from [2]).
is summarized in Fig.2 as “Ejection-Jet cycle”,
which has two significant properties:• Multi-scale: jet (∼ 10h, step (iv)), vortex ejection (∼ h/500, step (iii))• Convective instability (step (ii))
where h denotes the half width of the channel.

References[1] Toshiki Teramura and Sadayoshi Toh. Phys.Rev.E, 89(5):052910, May 2014.
[2] Toshiki Teramura and Sadayoshi Toh. arXiv (submitted to Phys.Rev.E) 2015.

Laser spectroscopic study of an atomic Bose-Hubbard
system with an atom-number-projection method
Quantum Optics and Laser Spectroscopy Group

Yusuke Nakamura

Abstract By developing a new method of atom-number-projection laser spectroscopy with an ultra-narrow
optical transition of ytterbium atoms, we successfully measure a two-particle correlation function from asuperfluid to Mott-insulating regime for various temperatures, revealing non-trivial behavior of thetemperature and interaction in a finite-temperature phase diagram of a Bose-Hubbard system.
© 2016 Department of Physics, Kyoto University

Ultracold atoms in an optical lattice attract considerable attention as a powerful experimental platform to study astrongly-correlated quantum many-body system in a highly controllable way1. One can finely control the temperature,
the strength of interaction, and atom number with an optical lattice system. Up to now, M. Greiner et al., and S.
Trotzky et al., observed a superfluid-Mott insulator (SF-MI) transition2 and a superfluid-normal fluid (SF-NF)
transition3 experimentally by measuring the matter-wave interference patterns of atomic clouds, respectively. Theseexperiments measure the 1st order correlation function, or a single particle density matrix, which is not sensitive tothe behavior of the system other than in a superfluid regime. On the other hand, a spectroscopic method, such asradio-frequency spectroscopy by G. Campbell et al. 4 or laser spectroscopy by S. Kato et al., could be utilized for the
study not only in SF but also in MI and NF regimes. In fact, S. Kato et al. performed laser spectroscopy across a
SF-MI transition. However, one needs the careful and sophisticated numerical simulation to extract interesting
physics of the system5.
In this work, by using an ultra-narrow optical transition (1S0-3P2) of ytterbium atoms, we established a new laser
spectroscopic method of atom-number-projection measurement, in which we suddenly ramp-up an optical latticepotential to quench an atom hopping and thus we can directly measure an atom number distribution in a lattice site as
well-resolved spectral peaks. A typical spectrum is shown in Fig. 1. From the measurement, we can deduce the 2nd〈〉 of an atomic Bose-Hubbard system over SF, MI and NF regimes fororder correlation function gvarious temperatures. Here,andrepresent annihilation and creation operators of an atom, respectively. From
the temperature dependence of g , we successfully revealed non-trivial behavior of the temperature and interaction
in a finite-temperature phase diagram of a Bose-Hubbard system. We will discuss the detail of the result.
(a)

(b)

Fig.1 Ordinary spectroscopy (a) and atom-number-projection spectroscopy (b). s is lattice depth.

References
1. I. Bloch et al., Rev. Mod. Phys. 80, 885-964 (2008); D. Jaksch et al., Phys. Rev. Lett. 81, 3108-3111 (1998).
2. M. Greiner et al., Nature 415, 39-44 (2002).
3. S. Trotzky et al., Nature 6, 998-1004 (2010).
4. G. Campbell et al., Science 313, 649-652 (2006).
5. K. Inaba et al., arxiv: 1507. 06399v1 (2015).

Dimer solid-liquid transition in thehoneycomb compound Li2-xRuO3
Quantum Materials Lab.

Marco Polo Jimenez Segura

Abstract: We study the variation of magnetic properties with the crystalline disorder and Li
content in Li2-xRuO3 containing Ru honeycomb lattice. We show how the unconventional
Ru-dimer liquid-solid transition below Td ~ 540 K depends on the quality of the samples. In
addition, we reveal the properties of a new phase with heavily deficient Li content.
© 2016 Department of Physics, Kyoto University

Since the discovery of the Ru-Ru dimer transition at Td ~ 540 K in Li2RuO3 [1], a number
theoretical and experimental groups have been focusing on understanding the precise nature of thisdimer transition [2]. Unlike the common Peirls transition proposed initially [3], a recent experiment,using high-energy x rays, suggests that the transition occurs because of the freezing of Ru-Ru
dimers from a dimer liquid into dimer solid [2]. Accordingly, a band-structure calculation [2]suggests that at high temperatures the ruthenium spins behave as spin 1/2. Thus, the predictions ofphases that exhibit topological superconductivity in honeycomb lattice with the spin S = 1/2 [4–6]have impulsed the search for superconductivity at low temperatures.
In the present work, we improved the quality of pristine samples and revealed that the magnetic
behavior with the dimmer transition exhibits a strong dependence on the crystallinity and on the cellparameters which vary with the preparation methods [7].
Furthermore, we study the magnetic properties of the de-lithiated “D-phase” Li2-xRuO3. The
D-phase is obtained by chemical oxidation of pristine samples using I2 dissolved in acetonitrile [8].
The change in the crystal structure is found to be congruent with previous studies [8]. Interestingly,
we find that the nature of the dimer transition is strongly dependent on the Li content.
Supports from the collaborators are appreciated: S. Kimber at ESRF, France, T. Fröhlic and M.
Braden at the Universität zu Köln, Germany, and A. Ikeda, S. Yonezawa and Y. Maeno in the
Quantum Materials lab, Kyoto University.
References[1] Y. Miura, Y. Yasui, M. Sato, N. Igawa, and K. Kakurai, J. Phys. Soc. Jpn. 76, 033705 (2007).
[2] S. A. J. Kimber, I. I. Mazin, J. Shen, H. O. Jeschke, S. V. Streltsov, D. N. Argyriou, R. Valentí, and D. I.
Khomskii, Phys. Rev. B 89, 081408 (2014).
[3] Y. Miura, M. Sato, Y. Yamakawa, T. Habaguchi, and Y. Ōno, J. Phys. Soc. Jpn. 78, 094706 (2009).
[4] Y.-Z. You, I. Kimchi, and A. Vishwanath, Phys. Rev. B 86, 085145 (2012).
[5] T. Hyart, A. R. Wright, G. Khaliullin, and B. Rosenow, Phys. Rev. B 85, 140510 (2012).
[6] D. D. Scherer, M. M. Scherer, G. Khaliullin, C. Honerkamp, and B. Rosenow, Phys. Rev. B 90, 045135(2014).
[7] Marco-Polo Jimenez-Segura, A. Ikeda, S. Yonezawa, and Y. Maeno, Phys. Rev. B submitted (2015).
[8] H. Kobayashi, R. Kanno, Y. Kawamoto, M. Tabuchi, and O. Nakamura, Solid State Ion. 86-88, 859 (1996).

The effect of the confinement into nano-micelleson the liquid crystalline orderSoft Matter Physics Group

Shinji Bono

Abstract We introduced smectic-A liquid crystals (SmA-LCs) into the core of nano-micelles, andinvestigated the effect of the confinement on the transition behavior of SmA-LCs. As a result, we foundthat the correlation length of the smectic layer is suppressed by confinement.
© 2016 Department of Physics, Kyoto University

Confinement effects change the physical nature of the soft condensed matter characteristic to intrinsic softnessof the order and large fluctuation. In liquid crystals (LCs), the confinement affects both the layer order ofsmectic-A (SmA)-LCs and the orientational order of nematic (N)-LCs. First, we fabricated N-liquid crystalline
nano-micelles (LCNMs) in which N-LCs are confined three-dimensionally into NMs with size of several hundred
nanometers, and investigated the N-isotropic phase transition behavior of LCs in NMs [1]. As a result, we foundthat the phase transition behavior changes from the first order to the second order owing to the confinement effect.
Next, we fabricated the SmA-LCNMs. SmA-LCs have the one-dimensional layer order together with
two-dimensional fluidity. We investigated the confinement effect on the SmA-N phase transition behavior of
SmA-LCNMs by measuring the temperature dependence of the correlation length of the layer order, . For theaccurate measurement of weak scattering from the tiny LCNMs, we performed synchrotron X-ray at FSBL03XU
of SPring-8.
Fig.1 shows the temperature dependence of  in NMs
together with that in the bulk state. The dashed and dottedlines indicate fitting curves by the power law, (T−TSmA-N)−,
where TSmA-N is the SmA-N phase transition temperature,and the critical exponent =0.48 is assumed as reported by
Ref.[2]. Since the SmA-N phase transition in the bulk stateis second order phase transition,  continuously diverges
toward TSmA-N on cooling. In the N phase just above TSmA-N,
 in NMs diverges in the same way as the bulk state. On theother hand,  is saturated below TSmA-N and is always
shorter than that of SmA-LCs in the bulk state (~1.0104
Fig.1 The temperature dependence of theÅ). In order to clarify the confinement effect on the layer
correlation length of the layer order
order in SmA-LCNMs, we measured as a function of thediameter of LCNMs, as shown in Fig.2. We controlled thediameter of NMs, 2R, by changing the ratio of SmA-LC tosurfactant [1]. The gray area below the dotted line indicatesthat the  is shorter than 2R.  proportionally increases as
2R increases, and is always shorter than 2R. Thus, it can beconcluded that the confinement suppresses  below the
SmA-N phase transition, though confinement does notaffect the development of the layer order in the N phase
under the condition that  is shorter than the diameter ofNMs.
Fig.2 The layer order correlation length
References
as a function of the diameter of the[1] S. Bono, et al., Europhys. Lett. 109, 26004 (2015)
LCNMs.
[2] Y. Kimoto, et al., J. Phys. Chem. B, 20, 6290 (2013)

Nuclear Magnetic Resonance Studies on
Heavy Fermion Superlattices
Quantum Materials Lab.

Takayoshi YAMANAKA

Abstract We investigated superlattice systems consisting of heavy-fermion (HF) compounds andconventional metals with nuclear magnetic resonance (NMR) microscopically. We succeeded inobserving NMR signals of each block layer (BL) and found that the interfaces between the HF andconventional-metal BLs play an important role in the superlattice.
© 2016 Department of Physics, Kyoto University

Heavy-fermion (HF) compounds are characterized by the strongly enhanced effective mass of itinerant
electrons due to the hybridization between localized f-electron and conduction bands at low temperatures. As aresult of the duality between itinerant and localized characters of f-electrons, various fascinating phenomena havebeen discovered. Recently, the technique of fabricating epitaxial superlattices consisting of HF compounds andconventional metals has been developed and provides us a new research field on f-electron systems [1,2]. For
example, in the superlattices consisting of HF superconductor CeCoIn5 and conventional metal YbCoIn5, thevalue of Hc2/Tc is much larger than that of bulk CeCoIn5, where Hc2 is the superconducting upper critical field at T
= 0 K and Tc is the critical temperature at μ0H = 0 T. In these superlattices, the superlattice structure characterized
by the heterostructure (Fig. 1) would play a key role, but the magnetic and electronic properties in each block
layer (BL) have not been explored at the microscopic level.
To investigate the magnetic and electronic properties in each BL of the superlattices, we have performed
nuclear magnetic resonance (NMR) measurement, which is one of the most suitable microscopic probes, on the
CeCoIn5(n)/YbCoIn5(5) superlattices as well as the thin films of CeCoIn5 and YbCoIn5, where n (= 5 or 9) layersof CeCoIn5 and 5 layers fixed of YbCoIn5. By comparing the NMR spectra of these samples, we succeeded in
identifying the 115In-NMR signals arising from the CeCoIn5 (Ce-) and YbCoIn5 (Yb-) BLs in the superlattices,
separately. From the measurements of nuclear spin-lattice
relaxation rate (1/T1) in each BL, we found that 1/T1 ofCe-BLs is systematically suppressed with decreasing
thickness of Ce-BL, although 1/T1 of Yb-BLs is essentiallyunchanged with 1/T1 of the YbCoIn5 thin film. The
unchanged 1/T1 of the Yb-BLs suggests that each BL isnearly isolated and the proximity of f-electrons with magnetic
moments to the nonmagnetic Yb-BL is unlikely to be theorigin of the reduction of 1/T1 of Ce-BLs. In addition, we
compared the NMR spectra obtained in the superlattices withdifferent thickness of the Ce-BLs, and identified 115In-NMR
signals arising from the interfaces and the inner layers. Fromthe measurement of 1/T1, we found that antiferromagnetic
fluctuations are spatially varied along the c-axis even in the
one Ce-BL and are significantly suppressed at the interface.
Taking into account of these results, we point out theimportance of the interfaces in these HF superlattices.
Fig. 1 The schematic image of the superlattices
References[1] H. Shishido, et al., Science 327, 980-983 (2010).
[2] Y. Mizukami, et al., Nature Phys. 7, 849 (2011).
[3] T. Yamanaka et al., submitted for publication.

of CeCoIn5(n)/YbCoIn5(5). The BLs of n-unit
cell thick CeCoIn5 and 5-unit cell thick YbCoIn5
are stacked alternately. The set of Ce-BL and
Yb-BL repeats several times.

Study of thermal Hall effect in a frustrated magnet
Laboratory for electronic properties of solids
Daiki Watanabe
Abstract We report that a two-dimensional kagomé insulator volborthite exhibit negative thermal Hall
conductivity κxy. We find that κxy is absent in the high-temperature paramagnetic state and develops inaccordance with the growth of the short-range spin correlations in the spin liquid state. The results
suggest the emergence of nontrivial excitations in the spin liquid which acquire fictitious magnetic flux.
© 2016 Department of Physics, Kyoto University

When quantum fluctuations suppress the underlying magnetic long-range order, a novel state so called a spin
liquid (SL) state often emerges. In such a state the constituent spins are highly correlated but still fluctuatestrongly down to much lower temperatures than the spin interaction energy scale, J. The low-energy properties inSL systems have been a long-standing mystery. The fluctuations of the spins in a SL have given rise to several
notions about novel collective phenomena, such as an emergent gauge field and fractional particle
excitations. Several exotic quasiparticles such as spinons and visons have been predicted theoretically. However,
the elementary excitations in SL states remain largely unexplored experimentally.
It has been shown that in the insulating quantum magnets, the thermal transport measurements can be used asa probe to unveil the ground state and quasiparticle excitations [1]. Recently, it has been pointed out that thethermal Hall measurements provide new insights into the exotic excitations in magnetic insulators. In magnetic
insulators there are no charged currents, and thus the magnetic field cannot exert a Lorentz force. However, thethermal Hall effect has been predicted in disordered magnets as a result of an emergent gauge field [2]. Veryrecently, it has also been reported in the disordered states but no discernible xy signal has been observed in SL
states. Thus the thermal Hall conductivity in SL states remains a matter of vital importance.
Volborthite, Cu3V2O7(OH)2⋅2H2O, is a magnetic insulator, in which 2D layer of Cu2+ has a distorted kagomé
structure with inequivalent interactions [3, 4]. The temperature dependence of magnetic susceptibility χ shows atypical behavior of 2D frustrated spin system. Below T* ~ 60 K, χ(T) begins to deviate from the Curie-Weissbehavior, implying that the spin correlations grow gradually when the temperature energy scale kBT* becomescomparable to the effective spin interaction energy Jeff. Due to the combination of strong geometrical frustration
with enhanced quantum fluctuations for S = 1/2, the magnetic ordering is suppressed down to TN ~ 1 K (~ 2K) atzero field (15 T), demonstrating the presence of an SL state in a wide temperature range TN < T < T* ~ Jeff/kB. χ
and C⁄T extrapolated to T = 0 above TN remains finite, suggesting the gapless spin excitations in the SL state.
Figure 1 depicts the temperature dependence of-κxy/TB at the field of 15 T [5]. Finite thermal Hall signal
appears at T ≲ T* ~ 60 K. The sign of κxy is negative, i.e.
electron-like. As the temperature is lowered, -κxy/TB firstdevelops gradually and then increases steeply below 30 K.
After reaching a maximum at around 15 K, -κxy/TB
decreases rapidly and changes the sign slightly above TN.
It should be stressed that no discernible thermal Hall
signal is observed in the paramagnetic state at T ≳ T* ~ 60
K. Moreover, -κxy/TB or -κxy exhibits a peak at around Tp
where becomes maximum due to the development of thespin-spin correlation length (see the inset of Fig. 1).
These results lead us to conclude that the observed
thermal Hall effect in volborthite arises from the magnetic Fig. 1. Temperature dependence of -κxy/TB at 15 T.
excitations in the SL state, not from phonons.
Inset shows -κxy at 15 T (left) and χ (right). The dotted
Referenceslines are guides to the eyes.
[1] M. Yamashita et al., Science 328, 1246 (2010).
[2] H. Katsura et. al., Phys. Rev. Lett. 104, 066403 (2010). [3] H. Yoshida et. al., Nat. Commun. 3, 860 (2012).
[4] H. Ishikawa et. al.,Phys. Rev. Lett. 114, 227202 (2015). [5] D. Watanabe et. al., submitted