平 成 ２ ５ 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

２０１４年１月２０日（月）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）
２０１４年１月２０日（月）９：００～

開始

目

次

１．The kinetic theory of lane formation
池田

昌浩（９：００）・・・・・

１

２．Non-Equilibrium Quantum Spin Transport Theory Based on Schwinger-Keldysh Formalism
仲田 光樹（ ９：２５）・・・・・ ２
３．Effect of Elastic Vibrations on Normal Head on Collisions of Isothermal Spheres村上亮（ ９：５０）・・・・・

３

４．Superconducting properties of heavy fermion thin films and superlattices
下澤 雅明（１０：１５）・・・・・

４

１０：４０～１０：５０

休憩

５．Nuclear Magnetic Resonance Studies of Iron Pnictide BaFe2(As1-xPx)2
家哲也（１０：５０）・・・・・

５

６．Field-induced nematic caps on the colloidal particles
内田隆之（１１：１５）・・・・・

６

７．Real-Time Detection of Transient Current Induced
by Femtosecond Pulse Excitation in Topological Insulators
大西 義人（１１：４０）・・・・・

７

１２：０５～１３：３０

昼休み

８．Molecular Dynamics Simulations of Nanobubbles on Substrates
河野 俊輔（１３：３０）・・・・・

８

９．Studying Spatial Distribution of Order Parameter in Superfluid
3He with Nuclear Magnetic Resonance Imaging
金本 真知（１３：５５）・・・・・

９

１０．Mode bifurcation of droplet motion under stationary laser irradiation
髙畠 芙弥（１４：２０）・・・・・１０
１１．In-plane anisotropy of the uniaxial pressure effect on the Mott insulator Ca2RuO4
谷口 晴香（１４：４５）・・・・・１１

１５：１０～１５：２０

休憩１２．Study of the electronic states in heavy fermion compound URu2Si2
利根川
１３．Antiferromagnetic ordering induced by paramagnetic
pair-breaking in strong-coupling superconducting states畠山

翔（１５：２０）・・・・・１２

雄気（１５：４５）・・・・・１３

１４．Spin-Triplet Superconductivity Induced by Ferromagnetic Fluctuations in UCoGe
服部 泰佑（１６：１０）・・・・・１４
１５．Structural and dynamical studies on the supra-protein complex in an active state森田

１７：００～１７：１０

有哉（１６：３５）・・・・・１５休憩

１６．Phase separation in a binary mixture confined between symmetricparallel plates: Capillary condensation transition near the bulk critical point
藪中 俊介（１７：１０）・・・・・１６
１７．Theoretical study of correlated topological insulators
吉田恒也（１７：３５）・・・・・１７

The kinetic theory of lane formation

Advanced statistical dynamics group

Masahiro Ikeda

Abstract We investigate pattern dynamics of a two-dimensional oppositely driven binary particle
system. A surprisingly rich dynamical behavior including lane formation, jamming, oscillation andturbulence-like dynamics is found using extensive particle-based simulations. We also develop the
kinetic theory based on Enskog equation to describe the lane formation process.
© 2014 Department of Physics, Kyoto University

Lane formation is one of the representative examples of
nonequilibrium phase transitions. When two kinds of particles are
driven in opposite directions, the system exhibits aself-organization from a uniformly mixed state into strongly
ordered anisotropic patterns. This driven segregation phenomenon,
first found in the computer simulations [1], has been observed inlaboratory experiments such as mixtures of oppositely charged
colloids [2]. Another important class of examples is pedestrian andtraffic flow dynamics. By tracing single-particle motions incolloidal dispersions, a recent paper suggested that the lane
formation takes place due to a "lock-in" mechanism [3]. The Fig. 1.
mobility of particles is initially isotropic by frequent collisions, The lane formation observed in thewhich, however, decreases considerably once the lane is formed. particle-based simulations
This microscopic dynamics leads to the trapping of particles within
the lanes and thus to the growth of the lane structures. This is also consistent with a physicalpicture employed in the phenomenological dynamic density-functional theory [4].
We show the instability of the lane formation observed by our simulation of a particle-basedmodel in which the self-propelling elements interact frictionally with the substrate [5]. A typicalsnapshot of the lane formation in this simulation is shown in Fig. 1.
We also develop the kinetic theory based on Enskog equation [6] to describe the lane formation
process for the counter driven dissipative particles. We have derived a set of hydrodynamic
equations for the density, the momentum current, and the kinetic temperature for a binary mixture
for the counter driven particles. We also characterize the interface between two stable phases ofdriven particles. Such a microscopic derivation of the driven particles is quite new, and thus, thederived equations are completely different from the conventional hydrodynamic equations.
We also try to discuss the instability for the straight interface between two phases in terms ofhydrodynamic equations derived from the kinetic theory. This research enables us to understandthe mechanism of various phenomena observed in our former numerical study of the lane
formation.
References[1] J. Dzubiella, G. P. Hoffmann, and H. Löwen, Phys. Rev. E 65, 021402 (2002).
[2] Mirjam E. Leunissen, et al, Nature 437 235 - 240 (2005).
[3] Teun Vissers, Adam Wysocki, et al, Soft Matter, 7, 2352 (2011).
[4] J. Chakrabarti, J. Dzubiella and H. Löwen, Europhys. Lett. 61 415 (2003).
[5] M. Ikeda, H. Wada and H. Hayakawa, EPL 99, 68005 (2012).
[6] V. Garzó and J. W. Dufty, Phys. Rev. E 59, 5895 (1999).

Non-Equilibrium Quantum Spin Transport Theory Based on
Schwinger-Keldysh Formalism
Physics of Matter: Condensed Matter Physics (YITP)

Kouki Nakata

Abstract We microscopically investigate the non-equilibrium quantum transport phenomena ofmagnetization on the basis of the Schwinger-Keldysh formalism. In particular, we clarify the microscopic
mechanism for the generation of the spin currents in metals and insulators and construct the theories.
© 2014 Department of Physics, Kyoto University

Owing to the indirect measurement by using the inverse spin-Hall effects [1], the spin current, which had been
simply the theoretical concept for a long time, was qualified as the physical quantity. Consequently, a new branchof physics called spintronics, whose central theme is the manipulation of spin degrees of freedom as well as
charge ones of electrons, has seen a rapid development over the last decades. Then, establishing the methods forthe generation of the spin currents and constructing the microscopic theory have become the significant issues
from viewpoints of both fundamental science and applications to information and communication technologies.
First, we reformulate the spin pumping theory on the basis of the Schwinger-Keldysh formalism, which can
explicitly treat the system out of equilibrium at finite temperatures, and construct the microscopic quantum spin
pumping theory [2]. Spin pumping is the experimentally established method [1] for the generation of the spincurrents and the spin pumping system is defined as the junction between the non-magnetic metal and theferromagnet. Although the spin pumping phenomenon is well understood at the level of the semi-classical theory[3], to microscopically describe the phenomenon has been an urgent issue. To obtain the understanding of spin
pumping beyond the semi-classical regime, on the basis of the spin continuity equation of the conduction
electrons, we microscopically describe the non-equilibrium spin-flip process arising from quantum effects at theinterface, where the exchange interaction between the conduction electrons and the magnons works. Consequently,
we clarify that spin pumping is characterized by the spin relaxation torque (SRT), which breaks the spinconservation law of the conduction electrons, and find that all information about the spin-flip processes and theapplied microwave are captured by the SRT. Then, the net pumped spin current, which can be regarded as the
non-linear response to the applied microwaves, is represented only in terms of the SRT. The distinction between
our quantum theory and the preceding semi-classical one is also clarified. In addition, we theoretically predict thatspin pumping is generated also by the electron spin resonance as well as the usual method via the ferromagnetic
resonance. This theoretical prediction is the important milestone to show the validity of our quantum theory.
After that, motivated by the breakthrough of the experimental techniques using the microwave pumping method[4], we show that the quasi-equilibrium Bose-Einstein condensation (BEC) of magnons occurs also in the
spin-pumping systems. To this aim, we construct a theory on the quasi-equilibrium magnon BEC where thethermalization processes, which work as a bridge between the magnon pumping driven by microwaves and theresultant magnon BEC, are phenomenologically taken into account. Magnon BEC is a macroscopic state withquantum coherence and is robust against the loss of information. On top of this, remarkably, the quasi-equilibrium
magnon BEC can be experimentally produced at room temperature by using the microwave pumping method.
Thus, we can make a bridge between the research on spintronics and magnon BEC and theoretically open a newdoor to experimentally exploring the spin current in the ferromagnetic insulators.
References[1] E. Saitoh et al., Appl. Phys. Lett., 88 (2006) 182509.
[2] K. Nakata, J. Phys. Soc. Jpn., 81 (2012) 064717., K. Nakata, J. Phys.: Condens. Matter., 25 (2013) 116005.
[3] Y. Tserkovnyak et al., Rev. Mod. Phys., 77 (2005) 1375.
[4] S. O. Demokritov et al., Nature, 443 (2006) 430.

Eﬀect of Elastic Vibrations on Normal Head on
Collisions of Isothermal Spheres
Advanced statistical dynamics group

Ryo Murakami

From the simulation of elastic sphere collisions, we ﬁnd that the restitution coeﬃcient e oscillates
against the impact speed due to the collision-vibration resonance. We also ﬁnd a sinusoidal behaviorof e against the initial phase in the eigenmodes for the collision of thermally activated spheres, whichcresults in e > 1. ⃝2014
Department of Physics, Kyoto Universitye

The impact processes play important roles in various ﬁelds ranging from
1
granular physics to nanoscience. The main aim of the research on impact
processes is to know the loss of the translational energy during the collision,
which is characterized by the restitution coeﬃcient e, the ratio of the re0.95
bound speed to the impact speed. There are three known mechanisms forthe loss of the translational energy, which causes e to be less than unity:(1) the excitation of vibration in the colliding object, (2) energy dissipation
0.9
due to the solid viscosity in the object, and (3) energy loss due to a plastic
0
0.1
0.2
0.3
0.4
deformation or fracture of the object [1]. Many papers (e.g. [2, 3]) dealedwith the mechanism (2) by applying the quasi-static theory in which themechanism (1) is ignored. References. [4, 5] investigated the mechanism (1) Figure 1: vCM dependence of e.
using two dimensional elastic disks. Here I address both the mechanisms (1)and (2) by using a model of isothermal visco-elastic spheres which is the natural extension of the previous 2Dmodel [4, 5]. In particular, I focus on the mechanism (1), and reveal the role of excited elastic vibrations duringcollisions. Thus, I restrict my interest to slow impacts, and ignore the mechanism (3) in the presentation.
Figure 1 shows the impact speed vCM dependence of e, where c(t) is the transverse sound speed for the
sphere [6]. I ﬁnd a characteristic oscillation of e(vCM ) which has never reported even in Refs. [4, 5]. From thedetailed analysis, I conﬁrm that this behavior arises from the resonance between the duration of contact andthe oscillation period of vibration of each mode [6].
There exists “super rebound” characterized by e > 1 for slow impacts
1.002
between nanoclusters at ﬁnite temperature [7]. Motivated by this ﬁndings,
I investigate the collision between a thermally activated sphere and a
1
ﬂat wall. In the super rebounds, a part of thermal energy is transferred
into the translational energy, which seems to violate the second law of
0.998
thermodynamics. However, Tasaki [8] indicated that super rebounds do
not conﬂict with the second law for impact processes, and the probability
0.996
-π
-π/2
0
π/2
π
of the restitution coeﬃcient satisﬁes an extended ﬂuctuation theorem. In
α020(0)the presentation, I numerically verify the extended ﬂuctuation theorem.
Figure 2 shows e against the initial phase of the quadrupole mode
α020 (0) for vCM (0) = 0.007c(t) and the temperature T = 2.14 × Figure 2: α020 (0) dependence of e.
10−8 M (c(t) )2 (300 K in the physical unit) [6]. I ﬁnd that a sinusoidal
behavior of e(α020 (0)) is responsible for super rebounds if vCM (0) is nearly equal to or slower than the thermal
speed. I reproduce the sinusoidal behavior from the perturbation theory of this system, and ﬁnd that therestitution coeﬃcient can exceed unity if the sphere expands to the axial direction at the instant of the impact.

References[1] K. L. Johnson, Contact Mechanics (Cambridge University Press, 1985).
[2] G. Kuwabara and K. Kono, Jpn. J. Appl. Phys. 26, 1230 (1987).
[3] N. V. Brilliantov, F. Spahn, J.-M. Hertzsch, and T. Pöschel, Phys. Rev. E 53, 5382 (1996).
[4] F. Gerl and A. Zippelius, Phys. Rev. E 59, 2361 (1999).
[5] H. Hayakawa and H. Kuninaka, Chem. Eng. Sci. 57, 239 (2002).
[6] R. Murakami and H. Hayakawa, submitted to Phys. Rev. E (arXiv:1309.095474).
[7] H. Kuninaka and H. Hayakawa, Phys. Rev. E 79, 031309 (2009).
[8] H. Tasaki, in The proceedings of the RIMS workshop ”Micro-Macro Duality in Quantum Analysis”, p. 102, Japan,
2006, No. 1507, RIMS, Kyoto University.

Superconducting properties of heavy fermion thin films andsuperlattices
Electronic properties of solids laboratory

Masaaki Shimozawa

Abstract We fabricate a new type of heavy fermion superconducting superlattices with thickness
modulations. We find that the modulations result in drastic changes of the upper critical field. The results
demonstrate that the introduced inversion symmetry breaking affects the nature of superconductivity
through the suppression of the Pauli pair-breaking effects.
© 2014 Department of Physics, Kyoto University

Heavy fermion materials are a specific type of intermetallic compound consisting of elements withf electrons. In these materials, the localized f electrons hybridize with the conduction electrons
through many-body effects. Hence, the quasiparticle effective mass in strongly enhanced at low
temperatures, and sometimes reaches a thousand times the mass of the bare electron. As a result of
the competition between itinerant and localized f electrons, a plethora of fascinating physicalphenomena including unconventional superconductivity with non-s-wave pairing symmetry appear
in the heavy fermion compounds [1]. The unconventional pairing symmetry and the associatedexotic superconducting properties have puzzled and fascinated researchers over the past quarter
century.
Recently, the Rashba splitting arising from the inversion symmetry breaking (ISB) has been
proposed to affect the superconductivity, giving rise to a variety of novel phenomena such as
anomalous magneto-electric effects and topological superconducting states [2]. It has also beensuggested that such phenomena are even more pronounced in strongly correlated electron systems[3]. However, the experimental study of the Rashba effect in heavy fermion systems has primarily
been performed using bulk single crystals, where the degree of the ISB is hard to be controlled
because it is determined by the crystal structure. Therefore, the systematic influence of the ISB on
unconventional superconductivity remains an open question.
Here, by using a state-of-the-art molecular beam epitaxy technology, we fabricate a new type ofheavy fermion superlattices, i.e. modulated superlattices in which the thickness of CeCoIn5 is kept
to 5, while the thickness of YbCoIn5 changes between m and m’ from one block layer to the next,
forming the c-oriented (5:m:5:m’) superlattices. For the m ≠ m’ superlattices, the additional ISB
along the c-axis can be introduced to the superconducting CeCoIn5 block layers. Through themeasurements of the temperature and angular dependencies of the upper critical field, we find asignificant suppression of the Pauli pair-breaking effect in these superlattices with introducing the
ISB. Further we revealed that the magnitude of this suppression increases with the degree of the
thickness modulation |m−m’|. These results demonstrate that the Rashba spin-orbit interaction ineach CeCoIn5 block layer is largely tunable by using the modulated superlattices. Our work paves
the way for obtaining novel superconducting states through the thickness modulation in the
superlattices with strong spin-orbit coupling [4].
References[1] C. Pfleiderer, Rev. Mod. Phys. 81, 1551 (2009).
[2] X. L. Qi and S. C. Zhang, Rev. Mod. Phys. 83, 1057 (2011).
[3] S. Fujimoto, J. Phys. Soc. Jpn. 76, 51008 (2007).
[4] M. Shimozawa et al., submitted for publication.

Nuclear Magnetic Resonance Studies ofIron Pnictide BaFe2(As1-xPx)2
Quantum Materials Laboratory

Tetsuya Iye

Abstract We present our nuclear magnetic resonance (NMR) studies of iron-based

superconductor (iron pnictide) BaFe2(As1-xPx)2. We have clarified quantum criticality,
microscopic coexistence and competition between magnetic and superconducting orderparameters, and orbital nematicity present in the tetragonal phase of this system.
© 2014 Department of Physics, Kyoto University

In this work, we focus on P-underdoped BaFe2(As1-xPx)2 showing antiferromagnetic orderings, which are lessstudied compared to the optimally-doped one. Since the superconductivity appears around the point where
antiferromagnetism is suppressed, it is quite important to understand magnetism as the background of theunconventional superconductivity. Static magnetic properties of BaFe2(As1−xPx)2 for 0.07 ≤ x ≤ 0.33 were
investigated by 31P-NMR spectrum measurement. The averaged magnetic ordered moment ‫ۦ‬mۧ at thezero-temperature limit estimated from the 31P-NMR spectrum shows a continuous suppression toward x ∼ 0.35
with increasing P concentration x, verifying a second-order quantum phase transition. This result provides
evidence of the existence of an antiferromagnetic (AFM) quantum critical point at x ∼ 0.35, consistent with thenormal state properties [1].
The coexisting state of magnetism and superconductivity is one of the most intriguing subject to study since themechanism of unconventional superconductivity is expected to be highly related to magnetic fluctuation [2].
31
P-NMR measurement on BaFe2(As1−xPx)2 for x = 0.20 at hydrostatic pressure of p ∼ 2 GPa was performed.
(T1T)−1 measurement on 31P nuclei in the AFM ordered state revealed that an SC transition occurs at the AFM
ordered site for x = 0.20 (p ∼ 2 GPa). This is the direct evidence of real-space coexistence of superconductivity
and antiferromagnetism in the microscopic scale. Moreover, 31P-NMR spectrum was found to become narrow
below Tc, indicative of the suppression of internal magnetic field due to the competition between SC and AFM
order parameters. Our results suggest that antiferromagnetism and superconductivity occur at the same Fermi
surfaces and compete with each other.
In the recent research field of iron pnictides, the electronic nematic state has been a hot topic in which theelectronic state spontaneously breaks the fourfold lattice symmetry in the tetragonal phase thus making various
physical properties twofold symmetric in the Fe plane [3]. Motivated by this, we measured in-plane fieldorientation dependence of 75As-NMR spectrum of single-crystal BaFe2(As1−xPx)2 above the structural phasetransition temperature TS. A large difference in the spectral linewidth between H || [100]o and H || [110]o in theorthorhombic basis revealed that in-plane anisotropy of the electric field gradient is present even in the tetragonalphase. This in-plane anisotropy arises from population imbalance between As-4px and 4py orbitals, which reaches |nx – ny | ~ 0.004 electron at T → TS. The orbital polarization is found to be further enhanced below ∼ 150 K,
which is consistent with the emergence of nematicity in torque and photoemission measurements. This result
indicates either a crossover in the magnitude/length of the orbital-nematic correlations, or a phase transition.

References[1] S. Kasahara et al., Phys. Rev. B 81, 184519 (2010). Y. Nakai et al., Phys. Rev. Lett. 105, 107003 (2010).
H. Shishido et al., Phys. Rev. Lett. 104, 057008 (2010).
[2] P. Dai et al., Nature Phys. 8, 709 (2012).
[3] J.-H. Chu et al., Science 329, 824 (2010). S. Kasahara et al., Nature 486, 382 (2012).

Field-induced nematic caps on the colloidal particles
Phase transition dynamics group

Takayuki Uchida

Abstract We numerically investigate effects of electric fields in a disordered nematogenic liquidcontaining dielectric particles. Because of the inhomogeneity of the permittivity, nematic domains
are stably formed near the poles of the particle in the electric field. These locally induced nematic
domains may change macroscopic properties of the disordered host media. For example, we
found Kerr effect of a nematogenic liquid can be drastically enlarged by adding a small amountcof dielectric particles. ⃝Departmentof Physics, Kyoto University
Electrostatic properties of nematic liquid crystals are very important from scientific and industrial viewpoints. In order to calculate a nematic order parameter Qij under a uniform electric field E0 , one usually
starts from an electrostatic free energy of the nematic liquid crystal [1],∫[]1Fe = −
dr ε0 E0 2 + ε1 Qij E0i E0j ,(1)8π
where ε0 and ε1 represent isotropic and anisotropic parts of the permittivity, respectively. However, eq.(1) issometimes inadequate because the electric field is not necessarily uniform. More precisely, the electric fielddepends on the nematic order parameter. So we should solve the Poisson equation (2) and the following formof the electrostatic free energy (eq.(3)) to obtain the precise electric field E [2,3]:∇i (εij Ej )
Fe′

L/2

(a)

= 0, εij = ε0 δij + ε1 Qij + εp δij ,∫1=
drεij Ei Ej .
8π
(b)
(c)
0.15

0

ford
fLdG
fgra
fele

-0.05
-0.1

-0.15
1.5

2

2.5

χ/χ0

3

f /(kBT/ξ )

1.3

0.05

-0.2 1

(3)

1.4

0.1

-L/2

(2)

no sphereR/ξ=30.0
43.5

1.2

1.1

1

3 3.5 400.2
~0.4 0.6 0.8
r/R
E0
Figure 1: (a) The profile of the nematic order parameter S = (3Qij Qji /2)1/2 and the director field. (b) The
profile of the scaled free energies. (c) The dependence of Kerr coefficient on the external electric field. L:
system size, R: sphere radius, ξ: coherent length of the nematogenic liquid, χ0 : Kerr cofficient in the uniform
system.

In this work, we study behaviors of a disordered nematogenic liquid containing a spherical colloid. The
medium is confined in a capacitor and equilibrated slightly above the isotropic-nematic transition temperature. The dielectric constant of the colloid is assumed to be much larger than that of the host liquid, εp = 20ε0 .
Then, we impose electric potential differences to the capacitor. We obtain an equilibrium state by numerically minimizing the Landau-de Gennes free energy and eq.(3) with satisfying eq.(2). When the potential
difference is sufficiently small, the medium is not ordered as usual. If the potential difference is larger than athreshold, nematic-isotropic transition occurs locally around the poles of the colloid. Although the total freeenergy density inside the ordered nematic domains is higher than that in the disordered state, the formed
nematic-isotropic interfaces are thermodynamically stable (Figure 1a). The formation of the nematic domains
is caused by the balance between the ordering free energy ford inside and outside the nematic domains (Figure 1b). We also found that the induced nematic domains may change macroscopic physical properties of
the host disorderd liquid. In Figure 1c, for example, we show a strongly nonlinear increase of the global
dielectric constant, or Kerr cofficient, above the transition point.
Reference[1] P. G. de Gennes and J. Prost, The Physics of Liquid Crystals (Clarendon, Oxford, 1993)[2] A. Onuki, J. Phys. Soc. Jpn 73, 511 (2004)[3] K. Tojo, A. Furukawa, T. Araki and A. Onuki, Eur. Phys. J. E 30, 55 (2009)

Real-Time Detection of Transient Current Induced
by Femtosecond Pulse Excitation in Topological Insulators
Solid State Spectroscopy Group

Yoshito Onishi

Abstract We have observed terahertz emission from three-dimensional topological insulators underillumination of the femtosecond pulse. The terahertz emission depends on the helicity of the excitation
pulse and the crystal-angle, indicating that the origin should be the surface current. A plausible candidate
for the surface current would be Floquet-Bloch state formation.
© 2014 Department of Physics, Kyoto University

Electric Field (mV/cm)

In three-dimensional topological insulators (TIs), nontrivial topology in the bulk insulating state results in thesurface electronic state following the massless Dirac equation and the spin state locked by the momentum
direction. Optically excited Dirac fermions provide us a good platform to study the non-equilibrium dynamics ofrelativistic particles interacting with electromagnetic field. Theoretical reports show that spin-selective excitation
by circularly polarized light induces asymmetrical distribution in k-space and drives macroscopic current [1].
Actually, current driven by circularly polarized light has been measured with two-terminal sensing [2]. However
symmetry breaking by an attachment of electrodes hinders understanding the driving mechanism. In addition,
time-resolved techniques are awaited to study transient dynamics of the induced surface current.
In this study, we have investigated transient dynamics of the photo-induced current with a contactlessmeasurement in three-dimensional TIs Bi2-xSbxTe3-ySey (= (0.5, 1.3) and (1, 2)). The current induced byfemtosecond pulse emits the electromagnetic wave in terahertz (THz) range. Here we have observed
electromagnetic emission proportional to time-derivative of the current driven by a femtosecond near-infraredcircularly polarized pulse (pulse width: 100 fs). Fig. 1(a) and (b) show horizontal (a) and vertical (b) componentsof the emitted THz waveform from Bi1.5Sb0.5Te1.7Se1.3 at azimuthal angle= 0 degree under the right- or lefthanded circularly polarized illumination, respectively. The emitted wave is horizontally polarized and the signs ofelectric field are opposite between the right- and left- handed circularly polarized excitation. In contrast, atazimuthal angle= -30 degrees the THz emission is vertically polarized shown in Fig. 1 (c) and (d). Detailed
azimuthal angle dependence of the THz polarization indicates that the polarization rotates synchronized with therotation of crystal with three-fold rotational symmetry, which isinconsistent with the conventional photogalvanic mechanism for(c)(a)
 = - 30
 = 0Horizontal
Horizontal
driving photocurrent [2]. Analysis of waveform in time-domain
makes it clear that lifetime of current is less than pulse width ofL
Left-Handed (L)excitation pulse.
To account for our experimental results, we propose a newR
Right-Handed (R)mechanism of driving photocurrent. Light irradiation effectively
6
modifies the electron band structures through virtual photon
 = 0(d) = - 30(b)
VerticalVerticalabsorption processes. In this photon-dressed state, called
4
Floquet-Bloch state, light can induce asymmetrically deformedL
2
Lband structure and induce macroscopic current, which we have0
numerically calculated. The good agreement between
RR
experimental and numerical results suggests that photocurrent on-2
the surface would be induced in non-equilibrium steady state-1012Delay Time (ps)where Dirac fermions are hybridized with an applied light field.
Fig.1 (a)-(d) Time-resolved waveforms
References
emitted from topological insulator[1] P. Hosur, Physical Review B 83, (2011).
Bi1.5Sb0.5Te1.7Se1.3 at azimuthal angle 𝜃 = 0[2] J. W. McIver, D. Hsieh, H. Steinberg, P. Jarillo-Herrero, and(a,b) and 𝜃 = -30 degrees (c,d).
N. Gedik, Nature Nanotechnology 7, 96 (2011).

Molecular Dynamics Simulations of Nanobubbles
on Substrates
Fluid Physics Group Shunsuke Kohno
Abstract We performed molecular dynamics simulations of shrinking process of nanobubbles onhydrophobic and hydrophilic substrates in three component Lennard-Jones systems and investigatedlifetime of nanobubbles. In the preparation of nanobubbles, we observed semi-cylindrical shaped bubc 2014 Department of Physics, Kyoto University
bles due to finite-size effects. ⃝Nanobubbles, which are considered to be one cause of characteristic behavior of fluids in microscopic
systems, have been extensively investigated in the past decades. Although their lifetime is theoreticallyestimated to be an order of µs with a simple diffusion model, the lifetime observed in experiments on thehydrophobic surfaces reaches to a few days. To explain this astonishingly long lifetime of nanobubbles,
many mechanisms have been proposed. However, no one turned out to be a dominant cause of their stability.
Recently, Lohse et al. proposed a new dynamic equilibrium model, in which the substrate plays an imporantrole. However, the origin of re-entrance motions of gas atoms is not clear.[1]To investigate effects of the substrate to the lifetime of nanobubbles, we performed MD simulations of
the shrinking process of nanobubbles in three component Lennard-Jones systems. Periodic boundary conditions are applied to the calculation box. Simulations consist of two steps. In the first step, the temperatureof systems is controlled to the one under which nanobubbles are sustained stably in the finite-sized calculation box. At the beginning of the second step, the temperature is suddenly raised to the one under which
steady nanobubbles cannot be created spontaneously, and nanobubbles begin to shrink immediately.
In the shrinking process of nanobubbles, the densities of liquid and gas atoms approach to the steadyvalues as shown in Fig.1. Nanobubbles on the substrate shrink relatively slowly compared with thosesurrounded by the bulk liquid. On the other hand, there is no remarkable difference between the lifetimesof nanobubbles on the hydrophobic and hydrophilic substrates.
In the first step, spherical-cap shaped nanobubbles are created on the hydrophilic substrate, and semicylindrical shaped nanobubbles are created on the hydrophobic substrate. When the hydrophobicity isdecreased from the hydrophobic state to the hydrophilic state, a semi-cylindrical bubble does not change its
shape. On the other hand, increasing the hydrophobicity from the hydrophilic state to the hydrophobic state,a spherical-cap shaped bubble changes its shape to semi-cylindrical at a certain hydrophobicity. Reducing
relative bubble volume, a spherical-cap shaped nanobubble changes its shape at higher hydrophobicity.
This strongly suggests that semi-cylindrical shaped bubbles are created due to finite-size effects.
(b) 20

1.0ns
3.0ns
5.0ns
7.0ns
9.0ns

2

1.5

210
18

3

17
16

1.0ns
3.0ns
5.0ns
7.0ns
9.0ns

15

0

0.2

0.4
0.6
z position

0.8

1

0

0.2

0.4

0.6

z position

0.8

200
190
180
170

Change shape

160

14

1

cylindrical cap
spherical cap

220

volume [nm ]2.5(c) 23019liquid density [nm-3]

gas density [nm-3]

(a) 3

1

150
0.3

0.4

0.5

0.6
εWL/εLL

0.7

0.8

0.9

Fig.1 (a) and (b): an example of time evolution of gas and liquid densities outside the bubble averaged
in 5 layers perpendicular to the wall. The hydrophobicity is controlled by ε WL /ε LL (W and L denote walland liquid, and ε is an strength of LJ interaction.). (c): the volumes of semi-cylindrical and spherical-cap
shaped bubbles for various hydrophobicity.

References[1] J.R.T.Seddon, D.Lohse, W.A.Ducker and V.S.J.Craig, Chemphyschem. 13, 2179 (2012)

Studying Spatial Distribution of Order Parameter in Superfluid3
He with Nuclear Magnetic Resonance Imaging
Low Temperature Physics Laboratory

Masatomo Kanemoto

Abstract Resonance frequency of NMR in superfluid 3He reflects the local orientation of internal
degree of freedom of the order parameter. I developed a method to measure the spatial distribution of theresonance frequency in order to study inhomogeneous order parameter in superfluid 3He.
2014 Department of Physics, Kyoto University

Superfluid 3He is a p-wave pair condensate with multiple internal degrees of freedom. So superfluid 3He has
multiple phases. In the A-phase, the order parameter is expressed by two vectors, d and l. In the B-phase, the orderparameter is expressed by n vector and a rotation angle θ. Order parameter may vary in space. The spatial
distribution of the order parameter is called as a texture. The texture is determined by minimizing the sum ofvarious energies. Dipole energy is the energy due to the dipole interaction acting on two spins which make pair.
Gradient energy comes from the spatial variation of the order parameter. Magnetic energy originates from theanisotropy in magnetic susceptibility. In addition, pair breaking effect near the boundary orients orbital angularmomentum of the pair to be perpendicular to the walls of the container.
An NMR signal in superfluid 3He is characterized by a frequency shift from Larmor frequency which isdetermined by applied magnetic field. The frequency shift varies in space because of the texture. For example, in
the A-phase, d and l orient parallel or anti-parallel with each other due to the dipole interaction. If there areparallel and anti-parallel domains there appears a region where d and/or l rotate gradually in space in order toconnect order parameters on each sides. This region is called as a domain wall. A frequency shift at the domain
wall is reduced compared to that from the bulk part. The existence of the domain wall is proven by NMR satellite
peak in the spectrum. However the actual shape of the domain wall in real space is not clearly studied. In the Bphase magnon BEC was observed at very low temperature. The observed irregular decay of the magnon BEC
suggested the presence of the domain wall as well. A phase boundary between the A-phase and the B-phase can bestabilized under magnetic field gradient. The texture near the phase boundary is not yet clearly understood. Thus a
new method to directly measure the shape of the texture in space is strongly awaited.
In standard MRI the spatial distribution is mapped onto the distribution of resonant frequency by applying amagnetic field gradient. In the case of superfluid 3He, it is impossible to obtain the image by this method because
we can not distinguish the frequency shift and the effect of applied magnetic field gradient. Therefore, wedeveloped a new technique called Magnetic Resonance Spectroscopic Imaging (MRSI). In MRSI, we obtain a setof NMR signals with various intensity of the magnetic field gradient G with identical direction. Then we canextract spatial distributions by Fourier transformation in G and then the frequency distributions by Fouriertransformation in time. The MRSI can be the first tool to study inhomogeneous texture.
As the first practical test of the MRSI, we did the experiment with liquid 3He in a parallel plate cell whose gap
was 100 micrometer. Figure 1 shows the measured frequency distribution in the normal phase under an
intensionally applied linear magnetic field gradient. Residual magnetic field distribution after canceling linear
field gradients in X,Y,Z directions is shown in Fig. 2. The saddle shaped distribution was consistent with thequadratic magnetic field distribution. Spatially integrated frequency distribution was in good agreement with thestandard NMR spectrum. MRSI measurement in the A-phase showed uniform frequency shift as expected in theparallel plate cell. Thus I could prove that MRSI measurement is applicable to the superfluid state.

Fig.1. Measured frequency distribution ω in a parallel plate cellz-p Quadratic
under linear
field
gradient along
p axis.
Fig.2.
field
distribution
ω aftercanceling linear fielMode bifurcation of droplet motion under stationary laser
irradiation
Dissipative Structure and Biological Physics

Fumi Takabatake

Abstract Self-propelled motion of an oil droplet induced by a local temperature gradient underlaser irradiation is investigated. With an increase in the laser power, droplet motion transitions
from rectilinear motion to rotary motion. This mode bifurcation is interpreted in terms of
spontaneous symmetry-breaking depending on the energy flux rate.
© 2014 Department of Physics, Kyoto University

Inhomogeneous temperature and/or chemical concentration at the interface generate tangential flow along theinterface, which is called Marangoni flow. When Marangoni flow is induced at a free fluid interface,self-propelled motions of the objects floating on the interface are generated by their interfacial tension gradient.
Such self-propelled object exhibits irregular motion called active Brownian motion under isotropic boundary
conditions. In contrast, by selecting a suitable boundary condition, e.g., internal or external asymmetry, it becomes
possible to extract regular motion with a specific mode according to its symmetry [1]. Furthermore, we recently
reported that self-propelled motion can undergo mode bifurcation depending on the degree of non-equilibrium
through spontaneous symmetry-breaking, even under boundary conditions with the same symmetry [2].
In order to verify the spontaneous mode bifurcation, we investigated a self-propelled motion of a mm-sized
droplet floating on water driven by local heating with a spatially-fixed laser. The motion of the oil droplet is
induced through the generation of shear flow due to interfacial tension gradient, i.e., thermal Marangoni
convection. It was found that the mode of the motion of the circular droplet bifurcates into qualitatively different
types of regular motion, i.e., rectilinear reciprocal motion and circular orbital motion, with an increase in theheating power (Fig. 1). The essential features of this mode-bifurcation are discussed in terms of spontaneous
symmetry-breaking under a high gradient of temperature, and are reproduced with simple ordinary differential
equations by incorporating a delay function of the Marangoni convection and heated position.

Fig. 1. (a) Trajectories of the center of the droplet. The mode of droplet motion changes from rectilinear
reciprocal motion to circular motion. The laser power was (a-1) 0.30 mW and (a-2) 1.00 mW. The volumeof the droplet was 20 μl. (b) The variation in translational kinetic energy per unit mass with respect to thelaser power.

References[1] S. Nakata, Y. Iguchi, S. Ose, M. Kuboyama, T. Ishii, and K. Yoshikawa, Langmuir 13, 4454 (1997).
[2] F. Takabatake, N. Magome, M. Ichikawa, and K. Yoshikawa, J. Chem. Phys. 134, 114704 (2011).

In-plane anisotropy of the uniaxial pressure effecton the Mott insulator Ca2RuO4
Quantum Materials Lab.

Haruka TANIGUCHI

Abstract The antiferromagnetic Mott insulator Ca2RuO4 exhibits various electronic states
depending on lattice distortions through strong coupling between the lattice and orbital degrees
of freedom. By in-plane uniaxial pressures, we newly induced ferromagnetic metallic phase.
Furthermore, we revealed substantial anisotropy in the uniaxial-pressure response. We discuss
the origin of these phenomena.
© 2014 Department of Physics, Kyoto University

The antiferromagnetic Mott insulator Ca2RuO4 exhibits drastic changes in its electronic states under external
stimuli such as isovalent Sr-Ca substitution, hydrostatic pressure, epitaxial stress in thin film, or electric field [1].
Such changes are caused because the orbital degree of freedom strongly couples with the lattice distortion. For
example, it has been known that ferromagnetic metallic (FM-M) phase emerges when the RuO6 octahedra in the
structure are elongated along the c axis [2]. Thus, we aimed to control the electronic state of Ca2RuO4, by using
in-plane uniaxial pressures, which stretch the lattice along the c axis more effectively. We measured the electric
resistance and magnetization under in-plane uniaxial pressures with two different pressure directions: parallel anddiagonal to the in-plane Ru-O bond of the RuO6 octahedra (we denote these directions as [100]T and [110]T,
respectively, using the tetragonal notation) [3]. We note that because of the orthorhombic distortion, twin domains
are formed with the twin boundaries running along the [100]T direction.
We succeeded in inducing the FM-M phase with in-plane
uniaxial pressures. The critical pressures of the FM-M phasefor the uniaxial pressure (0.4 GPa for P//[100]T and 0.2 GPa
for P//[110]T) are substantially lower than that for thehydrostatic pressure (0.5 GPa). This fact demonstrates theeffectiveness of the uniaxial pressure to control the electronic
state in Ca2RuO4. Interestingly, the critical pressures of the
FM-M state were found to be highly anisotropic: the criticalpressure for P//[110]T is only a half of that for P//[100]T. In
addition, the pressure dependence of the magnetization is alsoquite anisotropic as shown in Fig.1; In particular, underP//[110]T, the development of the FM component of themagnetization occurs twice from 0.2 to 0.4 GPa and above 1.2
Fig.1. Pressure dependence of ferromagnetic
GPa. These peculiar anisotropic results can be naturallycomponent of magnetization for Ca2RuO4 under
understood as a consequence of the orthorhombic crystal
in-planeuniaxial pressures along the [100]T or
distortions in Ca2RuO4 and existence of orthorhombic[110]T directions [3].
crystalline twin domains in the sample.

References[1] S. Nakatsuji et al., Phys. Rev. B 62, 6458 (2000); P. Alireza et al., J. Phys.: Condens. Matter 22, 052202 (2010);
X. Wang et al., Appl. Phys. Lett. 85, 6146 (2004); F. Nakamura et al., Sci. Rep. 3, 2536 (2013).
[2] O. Friedt et al., Phys. Rev. B 63, 174432 (2001); P. Steffens et al., Phys. Rev. B 72, 094104 (2005).
[3] H. Taniguchi et al., Phys. Rev. B 88, 205111 (2013).

Study of the electronic states in heavy fermion compound URu2Si2
Electronic properties of solids laboratory

Sho Tonegawa

Abstract We perform cyclotron resonance and high-resolution synchrotron X-ray experiments inthe “hidden order” phase of URu2Si2. Our results reveal that the Fermi surface breaks the crystal
four-fold symmetry and tiny orthorhombic lattice distortion sets in below the transition. This
places strong constraints on the symmetry of the hidden order parameter.
© 2014 Department of Physics, Kyoto University

The heavy fermion compound URu2Si2 exhibits a second order phase transition at 17.5 K

accompanying a huge amount of entropy loss, but no structural and magnetic ordering have been
observed. Despite considerable experimental and theoretical efforts for more than a quarter century,
the order parameter is not yet totally understood and therefore the phase is called “hidden order’’phase. In general, a second-order phase transition causes a change in various types of symmetries,
such as rotational, gauge and time reversal symmetries. Therefore the experimental determination of
broken symmetries is the most essential step toward elucidating the nature of the hidden order phasetransition. Recent magnetic torque and NMR measurements reveal the in-plane anisotropy ofmagnetic susceptibility [1,2], which suggests that the crystal four-fold rotational symmetry in thetetragonal URu2Si2 is broken below the hidden order transition. This newly suggested rotational
symmetry broken state (“nematic” state) has raised several theoretical proposals, and calls forfurther experimental verifications by using other techniques.
For the understanding of the nature of the “nematic” state, it is important to clarify how theelectronic structure is related to the rotational symmetry breaking. We therefore perform cyclotron
resonance measurements in the hidden order phase, which allow the full determination ofangle-dependent electron-mass structure of the main Fermi-surface sheets. Furthermore, we find ananomalous splitting of the sharpest resonance line under in-plane magnetic-field rotation. This ismost naturally explained by the domain formation, which breaks the fourfold rotational symmetryof the underlying tetragonal lattice. The results reveal the emergence of an in-plane mass anisotropy
with hot spots along the [110] direction, which indicates that the Fermi surface breaks the four-foldrotational symmetry in the hidden order phase [3,4].
Another important aspect of the “nematic” state is whether the rotational symmetry breaking is
induced by external magnetic field, because the torque, NMR and cyclotron resonance experiments
have been carried out under in-plane magnetic field [1-4]. We therefore perform high-resolution
synchrotron X-ray crystal-structure analysis at zero field for a high-angle (880) Bragg diffraction by
four-circle diffractometer. We find tiny but finite orthorhombic distortion of the order of 10-5 (orlattice constant change less than 100 fm), which suggests the four-fold rotational symmetry is
broken in the absence of magnetic field [5].

References[1] R. Okazaki et al., Science 331, 439 (2011).
[2] S. Kambe et al., Physical Review Letters 110, 246406 (2013).
[3] S. Tonegawa et al., Physical Review Letters 109, 036401(2012).
[4] S. Tonegawa et al., Physical Review B (in press).
[5] S. Tonegawa et al., submitted for publication.

Antiferromagnetic ordering induced by paramagnetic
pair-breaking in strong-coupling superconducting states
Condensed matter theory group

Yuhki Hatakeyama

Abstract We investigate the two-dimensional Hubbard model including the Zeeman energy with thefluctuation-exchange (FLEX) approximation in order to discuss antiferromagnetic ordering induced byparamagnetic pair-breaking (PPB) in strong-coupling superconductors. We also examine the influence ofthe strong-coupling effects on the PPB-induced antiferromagnetic ordering.
© 2014 Department of Physics, Kyoto University

Recently, field-induced enhancement of antiferromagnetism in d-wave superconductors with astrong paramagnetic pair-breaking (PPB) effect have been observed. In the high-field
low-temperature (HFLT) phase of CeCoIn5, an antiferromagnetic (AFM) order coexists with a
Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) superconducting (SC) order and is present only in the
HFLT phase[1]. An AFM order existing near the SC transition field Hc2(0) is also observed inpressurized CeRhIn5[2]. Moreover, a field-induced AFM quantum critical point (QCP) locatedslightly below Hc2(0) is suggested in many d-wave superconductors with a strong PPB effect.
Our previous study based on the weak-coupling BCS model[3] has shown that, in the high-fieldregion of a d-wave SC phase with strong PPB, an AFM order can be realized more easily than in
the normal state. The above observations can be explained on the basis of this mechanism. However,a SC state with strong PPB tends to be realized in materials with a strong electron correlation
and an AFM fluctuation, which are not incorporated in the weak-coupling BCS model, and theseeffects can affect the PPB-induced AFM ordering. Consequently, it is necessary to extend thetheory of the PPB-induced AFM ordering to the case of strong-coupling SC states.
In this study, we discuss the PPB-induced AFM ordering in strong-coupling SC states by investigating the two-dimensional Hubbard model including the Zeeman energy using the fluctuation-exchange (FLEX) approximation[4]. On the basis of the calculation of the transverse AFM
susceptibility, we show that the PPB-induced AFM ordering is realized in strong-coupling SC states
through the mechanism similar to that in the weak-coupling model. We also show that the PPB-induced
AFM ordering is affected chiefly by the following threestrong-coupling effects: the quasiparticle renormalization (i.e. the mass enhancement), the amplitude of
the SC order parameter, and the Stoner enhancement in
the normal state. We find that promotion of the
PPB-induced AFM ordering owing to the Stoner enhancement
dominate over the other two effects in the situation
close to an AFM-QCP. Therefore, an AFM order existing
only in the high-field region of the SC phase is expected
to be realized in d-wave superconductors with a strong
Fig. 1. H-T phase diagram obtained from
PPB effect close to an AFM-QCP.
the numerical calculation in thestrong-coupling model
References[1] K. Kumagai et al., Phys. Rev. Lett. 106, 137004 (2011).
[2] T. Park et al., Nature 440, 65 (2006).
[3] R. Ikeda et al., Phys. Rev. B 82, 060510 (2010); Y. Hatakeyama and R. Ikeda, Phys. Rev. B 83, 224518(2011).
[4] Y. Hatakeyama and R. Ikeda, arXiv:1309.4609 (to be published in J. Phys. Soc. Jpn.).

Spin-Triplet Superconductivity
Induced by Ferromagnetic Fluctuations in UCoGe
Quantum Materials Lab.

Taisuke HATTORI

Abstract We have investigated the relationship between ferromagnetism and superconductivity withusing NMR measurements on the ferromagnetic superconductor UCoGe. Our experimental results
strongly suggest that longitudinal ferromagnetic fluctuations play an important role for a pairing
mechanism of the spin-triplet superconductivity in UCoGe. © 2014 Department of Physics, Kyoto University
Identification of pairing mechanism leading to the unconventional superconductivity is one of the mostchallenging issues in condensed-matter physics. Therefore the discovery of superconductivity in the ferromagnet
UGe2 under pressure in 2000 had a great impact since we can investigate the relationship between ferromagnetic(FM) fluctuations and superconductivity. So far, four uranium FM superconductors have been reported: UGe2,
URhGe, UIr, and UCoGe.
In these FM superconductors, UCoGe is one of the most experimentally explored, because of the highest
superconducting (SC) transition temperature TSC ~ 0.8 K and lowest Curie temperature TCurie ~ 3 K at ambientpressure1. To clarify the relationship between ferromagnetism and superconductivity, we have performed nuclear
quadrupole resonance (NQR) / nuclear magnetic resonance (NMR) measurements on UCoGe. We have shownthat superconductivity occurs within the FM region, resulting in the microscopic coexistence of ferromagnetismand superconductivity2. Although the crystal structure is three dimensional, magnetic properties possess strong
Ising anisotropy with the c axis being the easy axis3. In addition, it is reported that the SC upper critical limiting
field Hc2 has also large anisotropy3,4: superconductivity survives with the external field as large as 15 T along thea and b axes, whereas along the c axis is as small as 0.5 T. This large Hc2 along the a axis is suppressed with asteep angle dependence when the field was tilted slightly from the a axis toward the c axis4. The observed
characteristic Hc2 behavior is one of the mysterious features of the superconductivity of UCoGe, and its origin
would be related to the mechanism of the superconductivity.
From the angle-resolved NMR measurements we showed that longitudinal FM fluctuations along the c axis are
dominant in UCoGe5. In addition, we found that these longitudinal FM fluctuations are well tuned by the external
magnetic field: the magnetic field along the c axis H || c suppresses the fluctuations drastically6. Interestingly thesetunable FM fluctuations seem to be related to thesuperconductivity since the anisotropy of the FM
fluctuations is well scaled to that of the superconductivity(Fig. 16). Combined with the theoretical model calculation,
the longitudinal FM fluctuations are strongly suggested to
be a SC pairing glue, concomitantly resolving theabove-mentioned puzzle of Hc2.

References[1] N. T. Huy et al., Phys. Rev. Lett. 99, 067006 (2007).
[2] T. Ohta et al., J. Phys. Soc. Jpn. 79, 023707 (2010).
[3] N. T. Huy et al., Phys. Rev. Lett. 100, 077002 (2008).
[4] D. Aoki et al., J. Phys. Soc. Jpn. 78, 113709 (2009).
[5] Y. Ihara et al., Phys. Rev. Lett. 105, 206403 (2010).
[6] T. Hattori et al., Phys. Rev. Lett. 108, 066403 (2012).

Fig.1 Hc dependence of magnetic fluctuations
along the c axis〈(dHc)2 〉at 1.7 K. Hc2 is alsoplotted against Hc.

Structural and dynamical studies on the supra-protein complex
in an active state
Biological Molecular Structure Group

Yuya Morita

Abstract The 26S proteasome is a huge molecular machine that degrades unnecessary proteins in theliving cell. We focused the catalytic domains of the 26S during the degradation process, and found that
26S has an exporting mechanism of the degraded peptides.
© 2014 Department of Physics, Kyoto University

The 26S proteasome is a ~2.5MDa molecular machine, and degrades unnecessary proteins at a metabolic
turnover in the living cell. It is composed of a barrel-shaped 20S core particle (CP) that is capped on both ends by
19S regulatory particle (RP). 20S is formed by axial stacking of four heptameric rings: 2 inner beta-rings and 2
outer alpha-rings. There are 3 active sites between 2 beta-rings, and 20S can degrade proteins when 1 or 2
alpha-rings of 20S are capped by 19S. One of the main questions is what occurs in the 26S conformational change
during the degradation process. There are some reports [1, 2] about 19S “rough” (~10Å) conformational changes
by electron microscopy during the degradation process, but there are few reports about 20S “precise” (~2.5Å)conformational changes as a part of the active 26S . Therefore, we investigated 20S conformational changes
between active and inactive states.
We added a detergent, Sodium Dodecyl Sulfate (SDS), to 20S in order to mimic the 20S conformation changes
as a part of the 26S at the protein degradation process. This “mimic 20S” structure was analyzed by X-ray crystal
structural analysis (resolution: 2.5Å). As a result, some holes on the side of 20S became larger and new
beta-strands were produced. These 20S conformational changes indicate that there exists and gives a mechanismin the 26S by which 26S exports unnecessary peptides from the produced side “dust holes”.
In addition, we verified our “dust hole model”, and approximately evaluated the dust hole size of 26S at thedegradation process. M. E. Matyskiela et al. [1] pointed out that 19S rotates by intrinsic angles when 26S degradesa substrate. We hypothesized that 26S was twisted by both 19S rotations. We approximated 26S as a cylindricalrigid body, and concluded the gap variation as 3±2Å.
Although there remain some important factors that were not taken into account, such as secondary structures,
our “dust hole model” reveals a mechanism that have not been pointed out by electron microscopic structural
analysis. In order to discuss our model more precisely, it is necessary to analyze 26S structure at ~2.0Å
resolution. We are trying to analyze 26S structure by X-ray structural analysis, and to construct the experimental
system to verify the effect of the “19S twist“ to the dust holes.

References[1] M. E. Matyskiela et al., NATURE STRUCTUAL & MOLECULAR BIOLOGY 20, 781-788 (2013).
[2] S. Bohn et al., PNAS 107, 20992-20997 (2010)[3] R. Beckwith et al., NATURE STRUCTUAL & MOLECULAR BIOLOGY 20, 1165-1172 (2013)

Phase separation in a binary mixture confined between symmetricparallel plates: Capillary condensation transition near the bulk
critical point
Phase Transition Dynamics Group	  	  Shunsuke Yabunaka
Abstract We investigate phase separation of near-critical binary mixtures between parallel symmetricwalls in the strong adsorption regime. We lower the temperature T below the capillary condensation linefrom above the capillary critical temperature and investigate the phase separation dynamics. A pancake
domain of the phase disfavored by the walls finally appears in the middle of the film.
© 2014 Department of Physics, Kyoto University	  The phase behavior of fluids confined in narrow regions has been studied extensively. It strongly depends onthe geometry of the walls and on the molecular interactions between the fluid and the walls. Its understanding is
crucial in the physics of fluids in porous media. It is also needed to study the dynamics of confined fluids. As oneof the simplest cases, we study the phase transition dynamics of a binary mixture confined between symmetricparallel plates [1].
We take into account the renormalization effect due to the critical fluctuations using the recent local functional
theory [2]. In statics, a van der Waals loop is obtained in the relation between the average order parameter ψ inthe film and the chemical potential when the temperature T is lower than the film critical temperature Tca . In
dynamics, we lower T below the capillary condensation line from above Tca , and calculate the subsequent timedevelopment assuming no mass exchange between the film and the reservoir. In the early stage, the order€€parameter ψ changes only in the direction perpendicular
to the walls. For sufficiently deep quenching, such€one-dimensional profiles become unstable with respect to the fluctuations varying in the lateral directions. The
late-stage coarsening is then accelerated by the hydrodynamic interaction. A pancake domain of the phase
disfavored by the walls finally appears in the middle of the film.

!

Fig. 1. The chemical potential obtained Fig. 2. Cross sectional velocity field v
from the 1D solutions with the average and order parameter field ψ in phaseorder parameter < ψ > .
separation.
€€

Fig. 3. Phase diagrams in the τ /τ D
- ψ m /ψ D plane in (a) and τ /τ D
- < ψ > /ψ D plane, where ψ m is the€References€[1] S. €Yabunaka, R. Okamoto, and A. Onuki, Phys. Rev. E 87 032405(2013).
[2] R. Okamoto and A. Onuki, J. Chem. Phys. 136, 114704 (2012)€

midpoint value.

€€Theoretical study of correlated topological insulators
Condensed matter theory group

Tsuneya Yoshida

Abstract After discovery of topological insulators, topological aspects of quantum phases have attracted
much interest. One of the current important issues is the correlation effect on these phases. In this study,
we address this issue by employing the dynamical mean field theory and the density matrix
renormalization group.
© 2014 Department of Physics, Kyoto University

In this decade, topological insulators have been found and provided a new arena of study incondensed matter physics. Recently, realizations of nontrivial insulators in d-, f- electron
systems are proposed (e.g, Na2IrO3, SmB6, LuPtSb, etc.), and the correlation effect on
topological insulators is one of the current important issues. Motivated by these studies, weaddress this issue by making use of nonperturbative methods and elucidate the following
behaviors.

(i) Mott transition in two-dimensional topological insulators. In the strongly correlated
region, Mott insulars, whose origin differs from that of band insulators, are realized. Thus, one
can ask how the topological insulator in the weakly correlated systems changes into a Mott
insulator. To address this issue, we employ the dynamical mean field theory (DMFT) and thecontinuous time quantum Monte Carlo method. Interaction dependence of the spin Hall
conductivity and the double occupancy reveals that the topological insulator changes into a
trivial Mott insulator via a first order transition [1]. This paramagnetic Mott transition is
expected to be observed in geometrically frustrated topological insulators such as Pr2IrO7.

(ii) Antiferromagnetic topological insulators. It is known that in the single-particle
framework, antiferromagnetic insulators can also possess nontrivial structures, but it is unclear
if such phases are realized even beyond the Hartree approximation. Our DMFT results clarify
that this type of nontrivial magnetic insulators is indeed realized in correlated systems [2].

(iii) Spin-selective topological Kondo insulators. The RKKY and the Kondo effects are
source of intriguing behaviors in heavy fermion systems. Recently, even for these systems
nontrivial insulators, called topological Kondo insulators, are proposed. In this study, we
address how these two essential effects affect topological phases and propose a new type ofquantum phases, spin-selective topological Kondo insulators, which are realized in aferromagnetic metallic phase and shows non-Tomonaga-Luttinger liquid behaviors at edges.
We expect that this exotic edge behavior can be observed by NMR experiments [3].

(iv) Topological Mott insulators in one dimension. In strongly correlated systems,
topological Mott insulators which host gapless spion excitations rather than electron
excitations at edges are proposed. Unfortunately, this type of quantum phase has not been
established yet, although various numerical analyses tried to find it. Our results obtained bydensity matrix renormalization group establish realization of this phase in a one-dimensional
system with the chiral symmetry. Furthermore, in this system, we observe a topological phasetransition without gap-closing in the single-particle excitation spectrum [4].
References[1] T. Yoshida et al., Phys. Rev. B 85 125113 (2012).
[2] T. Yoshida et al., Phys. Rev. B 87 085134 (2013).

[3] T. Yoshida et al., Phys. Rev. B 87 165109 (2013).
[4] T. Yoshida et al, submitted.