Download “New Horizons in Condensed Matter Physics”

International Symposium
“New Horizons in Condensed Matter Physics”
Sat 18 - Sun 19 June 2016
Koshiba Hall, the University of Tokyo
Abstracts
Organizing committee:
Shinji Tsuneyuki (chair, Univ. Tokyo)
Hideo Aoki (Univ. Tokyo & AIST)
Kazuhiko Kuroki (Osaka Univ.)
Philipp Werner (Univ. Fribourg)
Ryotaro Arita (RIKEN)
http://fpmrt.riken.jp/public_html/aoki.symposium/index.html
Overview
The Symposium is aimed to give an overview of various frontiers of condensed matter
physics and also to promote interdisciplinary exchange of ideas to and from cold-atom,
hadron and high-energy physics for future prospects.
Held under the auspices of Advanced Industrial
Science and Technology (AIST), Tsukuba, Japan
Supported by
KAKENHI Grant-in-Aid for Scientific Research (A):
Theoretical and experimental study of pressure- and nonequilibrium-control of high-Tc
superconductivity and its enhancement based on orbital distillation (FY 2014-2017)（PI:
H. Aoki）
Bulk-edge correspondence and its universality in topological phases --- From solid state
physics to cold atoms (FY 2014-2016)（PI: Y. Hatsugai）
Program
Day 1 (Saturday, June 18th, 2016)
13:30 - 13:35
Opening
Session I (Chair: H. Aoki)
13:35 - 14:20
F. Duncan M. Haldane (Princeton Univ.)
Composite bosons and fermions in a partially-filled Landau Level
14:20 - 15:05
Ryo Shimano (Univ. Tokyo)
Study of nonequilibrium responses in quantum matter - from QHE to
superconductor
15:05 - 15:50
Koji Hashimoto (Osaka Univ.)
Gravity challenges strongly correlated matter: Non-equilibrium phase diagram
15:50 - 16:10
Coffee Break
Session II (Chair: K. Held)
16:10 - 16:55
Hirosi Ooguri (Caltech & Kavli IPMU)
Gravitational Positive Energy Theorems from Information Inequalities
16:55 - 17:40
Hideo Aoki (Univ. Tokyo & AIST)
Perspective of superconductivity, topology and nonequilibrium
18:30 -
Banquet at Tokyo Kaikan Level XXI
Day 2 (Sunday, June 19th, 2016)
Session III (Chair: P. Werner)
9:00 - 9:45
Piotr Maksym (Univ. Leicester & Univ. Tokyo)
Graphene in External Potentials: Links with Atomic Physics and Optics
9:45 - 10:30
Yoshiro Takahashi (Kyoto Univ.)
Quantum simulation using ultracold atoms in an optical lattice
10:30 - 10:50
Coffee Break
10:50 - 11:35
Karsten Held (TU Wien)
Oxide heterostructures: from efficient solar cells to spin-orbit coupling
11:35 - 12:20
Jun Akimitsu (Okayama Univ. & Hiroshima Univ.)
Quo Vadis Superconductivity?
12:20 - 14:20
Lunch Break
12:20 - 14:20
Poster Session
Session IV (Chair: S. Tsuneyuki)
14:20 - 15:05
Ryotaro Arita (RIKEN CEMS)
High temperature superconductivity in light element materials
15:05 - 15:50
Philipp Werner (Univ. Fribourg)
Hund coupling effects in multi-orbital Hubbard systems
15:50 - 16:35
Kazuhiko Kuroki (Osaka Univ.)
Optimization of unconventional superconductivity through electron correlation
designing
16:35 -
Closing
Poster Session (12:20-14:20, Sunday)
P-01
Dai Kubota (Univ. Tokyo)
Approach to large cluster problems: Cellular dynamical mean field theory combined with realspace renormalization
P-02
Kanako Yoshizawa (RIST)
First principles simulation by using GUI software TAPIOCA and C-Tools
P-03
Masayuki Ochi (Osaka Univ.)
Accurate band structure of wurtzite ZnO calculated with the bi-orthogonal transcorrelated
method
P-04
Shiro Sakai (RIKEN)
Hidden fermionic excitations in strongly-correlated superconductors
P-05
Tomonari Mizoguchi (Univ. Tokyo)
Magnetic phase diagram in hyperkagome iridate Na4Ir3O8
P-06
Fumiya Sekiguchi (Univ. Tokyo)
“Mott transition” in excitonic system
P-07
Yosuke Nonaka (Univ. Tokyo)
X-ray magnetic circular dichroism and cluster-model analysis of the spinel-type vanadate
CoV2O4
P-08
Dongjoon Song (AIST)
Electronic Phase Diagram of Pr1-xLaCexCuO4- as Function of Electron Number Studied by
Angle Resolved Photoemission Spectroscopy
P-09
Masaki Tezuka (Kyoto Univ.)
Proposal for experimental realization and out-of-order correlation measurement of the
Sachdev-Ye-Kitaev model with ultracold gases
P-10
M. Horio (Univ. Tokyo)
Electronic structure of superconducting parent compound of T’-cuprate superconductors
Nd2CuO4 studied by hard X-ray photoemission and soft X-ray absorption spectroscopies
P-11
Motoharu Kitatani (Univ. Tokyo)
Superconductivity and Pomeranchuk instability in two-dimensional repulsive Hubbard model
P-12
K. Koshiishi (Univ. Tokyo)
Angle-resolved photoemission study of the electronic structure in the electronic “nematic”
phase of BaFe2As2
P-13
Naoto Tsuji (RIKEN)
Nonlinear optical response in electron-phonon coupled superconductors: Effects of Higgs
amplitude mode
P-14
Shunsuke Yamada (Univ. Tokyo)
A new method for calculating the one-electron energy spectrum of huge systems based on the
divide-and-conquer DFT method
P-15
Yasutomi Tatetsu (Univ. Tokyo)
Ab-initio study on transition-metal-doped Nd-Fe-B magnets
P-16
Sota Kitamura (Univ. Tokyo)
-pairing superconductivity in periodically-driven attractive Hubbard model
P-17
Nobuya Sato (Univ. Tokyo)
First-principles prediction of perovskite-type oxyhydrides ATiO2H (A = K, Rb, Cs) with a twodimensional electronic state
P-18
Ryosuke Akashi (Univ. Tokyo)
Magnéli-type phases as the missing link of the low-Tc—high-Tc superconducting phases in
compressed sulfur hydride
P-19
Taichi Hinokihara (Univ. Tokyo)
RISB study on f2-configuration quasiparticle systems
P-20
Masashi Tanaka (NIMS)
Direct Observation of Micro Structure on the Superconducting Single Crystals of KxFe2-ySe2
P-21
Daisuke Ogura (Osaka Univ.)
Two-Particle Self-Consistent Analysis for the Electron-Hole Doping Asymmetry of
Superconductivity in High-Tc Cuprates
P-22
Yuta Tanaka (Univ. Tokyo)
Nonthermal crystal-to-amorphous transition of Ge2Sb2Te5 by irradiating ultrashort pulse laser
P-23
Yutaka Akagi (Univ. Tokyo)
Topological Excitations in Frustrated Magnets
P-24
Hiroki Katow (Univ. Tokyo)
The Triexciton Stabilization in Indirect Gap Semiconductors
Session I-1
Composite Fermions and Bosons in a Partially-Filled Landau
Level
F. D. M. Haldane1,
1
Department of Physics, Princeton University, Princeton NJ 08544-0708 USA.
The key principle underlying both the incompressible fractional quantum Hall states
and the compressible composite-fermion Fermi liquids states is the emergent “quantum
geometry” of “flux attachment” that forms composite charged particles that couple to
emergent gauge fields that cancel their Bohm-Aharonov phases for motion in a
magnetic field, allowing rectilinear propagation. Recently, it has become apparent that
two emergent gauge fields (U(1) and SL(2,R)) play a key role, the second being the spin
connection of an emergent spatial metric that characterizes the shape of the “flux
attachment”.
The fundamental physics derives from the non-commutative geometry
of the residual guiding-center degrees of freedom of particles in a partially-filled
Landau level. Both the composite bosons that condense to form incompressible
fractional quantum Hall states, and the composite fermions that form a compressible
Fermi liquid exhibiting an “anomalous Hall effect” (generically present in Fermi
liquids in the absence of time-reversal symmetry), as in the case when the lowest
Landau level has filling =1/(even integer), can be understood from the quantumgeometric perspective.
Session I-2
Study of nonequilibrium responses in quantum matter
-from quantum Hall effect to superconductorRyo Shimano1,2
1
Cryogenic Research Center, The University of Tokyo, Yayoi, Bunkyo-ku, Tokyo 113-0032, Japan
2
Department of Physics, The University of Tokyo, Hongo, Bunkyo-ku, Tokyo 113-0033, Japan
Photoinduced nonequilibrium properties of condensed matter systems has gained
continuous interests over decades and now grown as a new paradigm in modern
condensed matter physics. The goal of these studies is the realization of quantum
control of material properties and the photo-creation of new matter phases. With the
advance of laser technology and sophisticated spectroscopic tools, these perspectives
are becoming more realistic. Among the variety of material systems, here I will present
our recent study on the nonequilibirum responses of two representative quantum matters
under the irradiation of coherent AC field: 1) quantum Hall systems and 2)
superconductors.
In the first subject, I will report on the optical quantum Hall effect, or equivalently
the quantum Faraday effect in a conventional (massive) 2D electron gas system [1] and
in a Dirac (massless) electron system in graphene [2]. In the second subject, I will report
on the observation of Higgs amplitude mode in s-wave superconductors. Although the
existence of collective amplitude mode in superconductors, namely the Higgs mode,
was predicted nearly a half-century ago soon after the development of BCS theory [3], a
clear experimental verification has remained unresolved. This is because the Higgs
mode in superconductors does not have an electric charge nor spin so that it does not
couple to the electromagnetic field. With the state of art ultrafast laser spectroscopy
technique, we overcome this difficulty and succeeded in the observation of Higgs mode
[4, 5]. The extension of the experiments to unconventional superconductors will also be
reported.
[1] Y. Ikebe, T. Morimoto, R. Masutomi, T. Okamoto, H. Aoki, and R. Shimano,
Phys. Rev. Lett. 104, 256802 (2010).
[2] R. Shimano, G. Yumoto, J. Y. Yoo, R. Matsunaga, S. Tanabe, H. Hibino, T.
Morimoto, and H. Aoki, Nature Commun. 4, 1841 (2013).
[3] P. W. Anderson, Phys. Rev. 112, 1900 (1958).
[4] R. Matsunaga, Y. I. Hamada, K. Makise, Y. Uzawa, H. Terai, Z. Wang, and R.
Shimano, Phys. Rev. Lett. 111, 057002 (2013).
[5] R. Matsunaga, N. Tsuji, H. Fujita, A. Sugioka, K. Makise, Y. Uzawa, H. Terai, Z.
Wang, H. Aoki, and R. Shimano, Science 345, 1145 (2014).
Session I-3
Gravity challenges strongly correlated matter :
Non-equilibrium phase diagrams
Koji Hashimoto1, Shunichiro Kinoshita2, Keiju Murata3 and Takashi Oka4,5
1
Department of Physics, Osaka University, Toyonaka, Osaka 560-0043, Japan
2
Department of Physics, Chuo University, Tokyo 112-8551, Japan
3
Keio University, 4-1-1 Hiyoshi, Yokohama 223-8521, Japan
4
Max-Planck-Institut f¨ur Physik komplexer Systeme (MPI-PKS), N¨othnitzer Straße 38, Dresden
01187, Germany
5
Max-Planck-Institut f¨ur Chemische Physik fester Stoffe (MPI-CPfS), N¨othnitzer Straße 40,
Dresden 01187, Germany
The renowned AdS/CFT correspondence
studied intensively in string theory provides
a novel tool for analyzing strongly coupled
quantum gauge theories. Effects of timedependent external fields on strongly
coupled theories can be studied by the
gravity duals, and here we report our results
on phase transitions caused by timedependent electric fields. The resultant
“dynamical phase diagrams” or “nonequilibrium phase diagrams” has an interesting
structure [1,2,3], showing that even with a very
small amplitude of the external fields the system
experiences phase transitions for finely tuned /
fast frequency. Instabilities for large external
fields can also be analyzed by the gravity dual
[4,5]. The QCD phase transition of
deconfinement is similar to the metal-insulator
phase transition, and we discuss implication to condensed matter physics.
[1] “Meson turbulence at quark deconfinement from AdS/CFT,” Koji Hashimoto,
Shunichiro Kinoshita, Keiju Murata, Takashi Oka, Nucl.Phys. B896, 738-762 (2015).
[2] “Turbulent meson condensation in quark deconfinement,” Koji Hashimoto,
Shunichiro Kinoshita, Keiju Murata, Takashi Oka, Phys.Lett. B746 311-314 (2015).
[3] “Electric Field Quench in AdS/CFT,” Koji Hashimoto, Shunichiro Kinoshita, Keiju
Murata, Takashi Oka, JHEP 1409 126 (2014).
[4] “Magnetic instability in AdS/CFT: Schwinger effect and Euler-Heisenberg
Lagrangian of supersymmetric QCD,” Koji Hashimoto, Takashi Oka, Akihiko Sonoda,
JHEP 1406 085 (2014).
[5] “Vacuum Instability in Electric Fields via AdS/CFT: Euler-Heisenberg Lagrangian
and Planckian Thermalization,” Koji Hashimoto, Takashi Oka, JHEP 1310 116 (2013).
Session II-1
Gravitational Positive Energy Theorems from Information
Inequalities
Hirosi Ooguri1.2
1
Walter Burke Institute for Theoretical Physics, California Institute of Technology, USA
2
Kavli IPMU, The University of Tokyo, Japan
Session II-2
Perspective of superconductivity,
topology and nonequilibrium
Hideo Aoki1,2
1
Department of Physics, The University of Tokyo, Hongo, Tokyo 113-0033, Japan
2
Electronics and Photonics Research Institute,
Advanced Industrial Science and Technology (AIST), Tsukuba, Ibaraki 305-8568, Japan
Email: [email protected] http://cms.phys.s.u-tokyo.ac.jp/en/index.html
I shall give a perspective in condensed-matter physics (CMP), conceived over 38
years of research carrier and culminating in recent works of mine. The developments
kicked off by the high-Tc superconductivity (HTC) and quantum Hall effect (QHE) in
the 1980s have given, and are still giving, fascinations that are remarkable in the long
history of CMP. HTC has introduced the concept of electron correlation, and is
witnessing unexpected diversifying into the iron-based and light-element
superconductivity. The topological system, which was historically initiated by QHE, is
also widening its horizon into topological superconductivity, physics of graphene, etc.
CMP realisations of field-theoretically interesting phenomena also abound.
Another impetus comes from high-performance computations, enabling us to
accurately understand the existing materials (e.g. the Tc dome), and to further perform
materials design, e.g. for higher Tc or topological systems. Cold-atom systems, with
their unprecedented controllability, are making idealized models experimentally feasible.
A recent important avenue is nonequilibrium physics, which realises novel quantum
phases unimaginable in equilibrium.
This applies to all of correlation,
superconductivity and topological properties for nonequilibrium phase transitions, such
as Floquet topological insulator and repulsion-attraction conversion, along with
nonlinear phenomena such as the Higgs-mode-resonated THG in superconductors.
These streams, closely linked with each other as below, are envisaged to provide future
perspectives. During the talk I shall describe various collaborations with many people,
both theoretical and experimental.
Superconductivity
correlation effect
HTC cuprate,
Iron-based,
Light-element, …
Topological SC,
paired FQHE state
Ferromagnetism,
supersolids, …
Noneq SC
Topological states
Correlation
Topological
Mott I
Dielectric breakdown
of Mott's insulator
Nonequilibrium
― QHE, graphene
IQHE,/FQHE, Graphene,
Cold atom physics, …
Floquet topological insulator
Noneq SC,
noneq phase transitions, …
Session III-1
Graphene in External Potentials: Links with Atomic Physics and
Optics
P. A. Maksym1,2 and H. Aoki1,3
1
Department of Physics, The University of Tokyo, Hongo, Bunkyo-ku, Tokyo 113-0033, Japan
2
Department of Physics and Astronomy, University of Leicester, Leicester LE1 7RH, UK
3
Electronics and Photonics Research Institute, AIST,Tsukuba, Ibaraki 305-8568, Japan
The new physics of graphene in external potentials is discussed. Single layer
graphene has a massless Dirac cone band structure. However a gap opens up when the
graphene is placed on an appropriate substrate such as hexagonal boron nitride. In the
presence of an external potential this system becomes a quantum dot, a device that
confines single electrons on a nanometre scale. The graphene dot is a close analogue of
a relativistic atom, with the important feature that the strength of the confining potential
is experimentally tunable. This enables the atomic charged vacuum to be investigated in
a solid-state device.
The charged vacuum is the last untested prediction of quantum electrodynamics [1].
If the nuclear charge of a hydrogenic atom is increased, the bound states decrease in
energy and cross the edge of the positron continuum at a critical charge of about 172. If
the bound state is occupied this is predicted to result in a negatively charged vacuum
and spontaneous positron emission. However, despite intense effort, this effect has not
yet been observed in an atomic system. In contrast, it should be easily observable in the
solid state [2,3].
Another advantage of the solid state analogue is that it is very sensitive to a
magnetic field. External magnetic fields only influence the atomic charged vacuum at
astrophysical magnetic fields of about 1010 T. However the graphene charged vacuum is
influenced by laboratory fields of around 1 T. Remarkably, the vacuum partly
discharges at a critical field and further increase of the field results in a re-entrant series
of charging and discharging cycles.
In bilayer graphene, the novel physics lies in the scattering states. With suitable
inter-layer bias, the propagating states exhibit two distinct phase velocities. This results
in electronic birefringence. There are also two group velocities, one of which is negative,
and this results in negative refraction. The combination of birefringence and negative
refraction is seldom found in optical media and its consequences are largely unexplored.
One of them is that a potential barrier splits a single stream of current into two separate
streams [4].
[1] J. Rafelski , L. P. Fulcher and A. Klein, Phys. Repts. 38, 227 (1978).
[2] P. A. Maksym and H. Aoki, Phys. Rev. B 88, 081406 (R) (2013).
[3] P. A. Maksym and H. Aoki, J. Phys. Conf. Ser. 456, 012026 (2013).
[4] P. A. Maksym and H. Aoki, in preparation.
Session III-2
Quantum simulation using ultracold atoms in an optical lattice
Yoshiro Takahashi
Department of Physics, Graduate School of Science, Kyoto University, Oiwakecho, Kitashirakawa,
Sakyo-ku, Kyoto 606-8502, Japan
A system of ultracold atoms in an optical lattice is an ideal quantum simulator of a
strongly correlated quantum many-body system and also a topological quantum system
due to the high-controllability of system parameters.
We recently investigate behaviors of ultracold atoms in an optical Lieb lattice which
has a novel band structure with a Dirac cone and a flat band [1]. In particular, a flat
band is important for generating novel quantum states such as a flat band ferromagnetic
state for fermions and a super-solid state for bosons. We successfully load ultracold
bosons into a flat band and study the dynamics characteristic of the flat band.
We also study topological charge pumping of ultracold fermions in a dynamical
optical super-lattice [2]. With this setup, we can simulate a Rice-Mele model in which
time-dependent potential depths and hopping strengths are introduced in a staggered
form. Charge pumping is directly measured as a shift of an atom cloud. In particular, a
topological nature of this charge pumping scheme is revealed by the measurements with
various trajectories of system parameters.
Furthermore, we have recently developed a quantum gas microscope for ytterbium
atoms with Faraday imaging or polarization phase-contrast imaging as well as ordinary
fluorescence imaging[3]. The behaviors of Bose-Hubbard system in the presence of
strong dissipation are also studied.
In this talk, I will report on these experiments in detail.
[1] S. Taie, et al, Science Advances, 1,10, e1500854(2015).
[2] S. Nakajima et al, Nature Physics. 12,296 (2016).
[3] R. Yamamoto et al, New J. Phys. 18,023016 (2016).
Session III-3
Oxide heterostructures: from efficient solar cells to spin-orbit
coupling
Karsten Held
Institute for Solid State Physics, Vienna University of Technology, 1040 Wien, Austria
Heterostructures made of transition metal oxides are emerging class of materials
which may replace at some point conventional semiconductors for specific applications.
We have developed a density functional theory plus dynamical mean field theory
(DFT+DMFT) approach for such heterostructures.
In the first part, I will show how to exploit the unique properties of these
heterostructures for high-efficiency solar cells [1]: The intrinsic electric field of polar
heterostructures allows for efficiently separating the created electrons and holes.
Furthermore, the heterostructure naturally provides electrical contacts through ultra-thin
conducting interface layers. The bandgap in some heterostructures is optimal for the
solar spectrum and can be tuned by using different chemical elements layer-by-layer.
Last but not least electronic correlations can give rise to impact ionization [2] and may
hence help to overcome the Shockley-Queisser limit of 39% efficiency.
In the second part, I will present the theory of spin-orbit coupling in oxide
heterostructures [3] which, due to multi-orbital effects, is strikingly different from the
standard Rashba theory of semiconductor heterostructures, and discuss prospects to use
SrVO3 heterostructures as a Mott transistor [4].
[1] E. Assmann et al., Phys. Rev. Lett. 110, 078701 (2013).
[2] P. Werner, K. Held, and M. Eckstein, Phys. Rev. B 90, 235102 (2014).
[3] Z. Zhong et al. Phys. Rev. B 87, 161102(R) (2013);
Mater. Interfaces, 1400445 (2015).
[4] Z. Zhong et al., Phys. Rev. Lett. 114, 246401 (2015).
Session III-4
Quo Vadis “Superconductivity” ?
－ Where is the “Room Temperature Superconductor” ? －
Jun Akimitsu
Research Institute for Interdisciplinary Science, Okayama University
Center for Chiral Science Hiroshima University
Superconductors can be categorized into three groups, depending on it’s Tc, “Matsu”
(Tc≳160K), “Take” (150K≳Tc≳77K) and “Um𝑒̀ ” (T≲77K).
Recently, new superconductor SH3(Tc⋍200K) has been discovered under high pressure,
which belongs to first “Matsu” group. This is a good chance to revisit to the road to the
room temperature superconductor.
My story has two parts
1) What we have learned from the history in the past.
2) Where is the room temperature superconductor ?
Session IV-1
High-temperature superconductivity in light-element materials
Ryotaro Arita
RIKEN Center for Emergent Matter Science, RIKEN, Wako, Saitama 351-0198, Japan
The history of superconductivity began with Kamerlingh–Onnes’s observation that
elemental mercury (Hg) loses electric resistance below Tc=4.2K. This seminal discovery
was soon followed by studies on other heavy elements; Tin (Sn) with Tc=3.7K, lead
(Pb) with Tc=7.2K, and so on. On the other hand, light elements do not seem promising
with regards to superconductivity; Tc of beryllium (Be) is 26mK and that of lithium (Li)
is 0.4mK [1].
However, the situation becomes totally different when light elements come together
to form compounds. Although magnesium (Mg) and boron (B) do not exhibit
superconductivity at ambient pressure, MgB2 becomes a superconductor at 39K [2].
With doping of alkali atoms, solid C60 converts from a semiconductor into a
superconductor with the highest Tc (~40K) among molecular solids.
Pressure effect on Tc can also change the situation dramatically. Under high
pressures (P~30GPa), Tc of Li increases by more than four orders of magnitude and
reaches ~20K [3]. It has been reported that highly compressed H2S becomes
superconductive at 203K [4].
Recently, we succeeded in reproducing the experimental high-Tc’s in Li, H3S and
alkali-doped fullerides (A3C60) with remarkable accuracy, without using a priori
information other than the crystal structure. There, we found that it is indispensable to
go beyond the standard Migdal-Eliashberg theory. For Li, the plasmon mechanism that
exploits the frequency dependence of the screened Coulomb interaction considerably
enhances pairing instability [5]. The effects of quantum zero point motion, phonon
anharmonicity, and higher-order electron-phonon scattering also play crucial roles in
sulfur hydrides [6]. For A3C60, we can understand why the superconducting phase
resides next to the Mott insulating phase in the phase diagram by considering the highly
non-trivial interplay between the local Coulomb correlations and electron-phonon
coupling [7]. In this talk, I will report on these studies in detail.
[1] J. Tuoriniemi et al., Nature 447 187 (2007).
[2] J. Nagamatsu et al., Nature 410 63 (2001).
[3] K. Shimizu et al., Nature 419 597 (2002); V.V. Struzhkin et al., Science 298 1213
(2002); S. Deemyad et al., Phys. Rev. Lett. 91 167001 (2003).
[4] A. P. Drozdov et al., Nature 525 73 (2015).
[5] R. Akashi and R. Arita, Phys. Rev. Lett. 111 057006 (2013)
[6] W. Sano, T. Koretsune, T. Tadano, R. Akashi and R. Arita, Phys. Rev. B, 93 094525
(2016); R. Akashi, M. Kawamura, S. Tsuneyuki, Y. Nomura and R. Arita, Phys. Rev. B
91 224513 (2015)
[7] Y. Nomura, S. Sakai, M. Capone and R. Arita, Science Advances, 1 e1500568
(2015), J. Phys. Cond. Matt, 28 153001 (2016)
Session IV-2
Hund coupling effects in multi-orbital Hubbard models
Philipp Werner
Department of Physics, University of Fribourg, 1700 Fribourg, Switzerland
I will discuss the spin-freezing phenomenon in multi-orbital systems with Hund
coupling and show that it is important for understanding the electronic structure of
strontium ruthenates and iron pnictides. The fluctuating local moments at the border of
the spin-frozen regime furthermore induce exotic ordered states such as spin-triplet
superconductivity and spin-orbital order. In models with negative Hund coupling,
relevant for the description of fulleride compounds, there is an analogous orbitalfreezing crossover, which can be linked to the spin-singlet superconducting instability
near the paired Mott state. Spin/orbital freezing thus emerges as the key mechanism
behind the unusual properties of correlated multi-orbital systems.
Session IV-3
Optimization of unconventional superconductivity through
electron correlation designing
Kazuhiko Kuroki
Department of Physics, Osaka University, Machikaneyama, Toyonaka, Osaka 560-0043, Japan
30 years have passed since the discovery of the high Tc superconductivity in the
cuprates. The simplest model that is considered to capture the essence of the cuprate
superconductors is the single orbital Hubbard model. Various studies suggest
occurrence of d-wave superconductivity in this model with a superconducting transition
temperature (Tc) of O(0.01t), where t is the nearest neighbor hopping integral. Although
this energy scale is very small compared to the original energy scale of the electrons, it
does correspond to Tc ～100K when t~ 1eV.
Around the year 2000, we proposed that Tc can be raised up to 0.1t in models which
possesses electron and hole disconnected Fermi surfaces. One of such is a bilayer model
with one orbital per site (multiband but single orbital), where the interlayer hopping is
larger than the intralayer ones [1]. It was a toy model that does not correspond to any
known actual material. Some years later, the iron-based superconductors were
discovered [2], and surprisingly and interestingly, they possessed disconnected electron
and hole Fermi surfaces. As will be shown in the talk, the iron-based superconductors
share some commonalities with the bilayer model, but a large difference is that they are
essentially multiorbital systems [3]. In fact, Tc of these superconductors is not as high as
0.1t either experimentally or theoretically.
Related to this issue is our study on the material dependence of Tc in the cuprate
superconductors. There, we have proposed an idea "orbital distillation" as a general
path to enhance Tc ; namely, single orbital systems can have higher Tc than multiorbital
ones in superconductors where Cooper pairing interaction originates from the
intraorbital Hubbard U[4]. This will also be explained in the talk.
Some while ago, we proposed another single orbital model as a candidate for systems
with Tc～0.1t, namely, a two-band system with narrow and wide bands[5]. In this
system, the light-mass electrons in the wide band can form Cooper pairs using strong
glue mediated by the large density of states in the narrow band. We will show how such
a situation may be realized in ladder-type lattices.
[1] K. Kuroki, T. Kimura and R. Arita, Phys. Rev. B 66, 184508 (2002).
[2] Y. Kamihara et al., J. Am. Chem. Soc. 130, 3296 (2008).
[3] K. Kuroki et al.,Phys. Rev. Lett. 101, 087004 (2008).
[4] H. Sakakibara et al., Phys. Rev. B 86, 134520 (2012).
[5] K. Kuroki, T. Higashida, and R. Arita, Phys. Rev. B 72, 212509 (2005).
P-01
Approach to large cluster problems: Cellular dynamical mean
field theory combined with real-space renormalization
Dai Kubota1, Shiro Sakai2, and Masatoshi Imada1
1
Department of Applied Physics, The University of Tokyo, Hongo, Bunkyo-ku, Tokyo 113-0033,
Japan
2
Center for Emergent Matter Science, RIKEN, Hirosawa, Wako, Sitama 351-0198, Japan
Strong correlation effects generate various phenomena, such as the Mott metalinsulator transition and high-temperature superconductivity. One of the useful methods
widely explored in correlated models to study these phenomena is cellular dynamical
mean field theory (CDMFT) [1], which solves a lattice model by mapping it onto a
cluster impurity model coupled to a fermionic bath (see the following figure). However,
the CDMFT simulations with a large cluster have been a numerical challenge since the
computational cost rapidly increases with the cluster size.
We propose a real-space renormalized DMFT (rr-DMFT) [2] as an approach to solve
large cluster problems efficiently. The rr-DMFT solves a large cluster model by
decomposing and mapping it onto multiple small cluster problems where we trace out
sites with a real-space renormalization. The following figure illustrates a case of solving
a 16-site cluster model with a 2-site impurity solver only. The computational cost is
considerably reduced by this procedure in comparison with the CDMFT. We benchmark
the rr-DMFT in the two-dimensional Hubbard model on a square lattice through
calculating the self-energy, spin structure factor, density of states and the Mott metalinsulator transition and show its improved efficiency and accuracy.
[1] G. Kotliar, S. Y. Savrasov, G. Pálsson, and G. Biroli, Phys. Rev. Lett. 87, 186401
(2001).
[2] D. Kubota, S. Sakai, and M. Imada, Phys. Rev. B 93, 205119 (2016).
P-02
First principles simulation by using GUI software TAPIOCA and
C-Tools
Kanako Yoshizawa1, Yoshihide Yoshimoto2, and Shinji Tsuneyuki3
1
Research Organization for Information Science and Technology, Kobe 650-0047, Japan
2
Grad. Schl. of Information Sci. and Tech., The Univ. of Tokyo, Tokyo 113-0033, Japan
3
Department of Physics, The University of Tokyo, Tokyo 113-0033, Japan
We develop GUI software TAPIOCA [1] and C-Tools [2], to improve the usability of first principles
simulation codes for materials.
TAPIOCA is a support software to enhance the usability of a DFT code xTAPP [3] by visualization.
The GUI input and 3DCG output allow you to easily perform xTAPP calculation and understand the
results. Screenshots of TAPIOCA for TiO2 charge density is shown in fig. 1.
There are a variety of DFT codes with each strength, and to combine the strength we have to transfer
among the codes. For this purpose, we have developed an input format conversion system, named as CTools, with a developed unified input format in XML as a common interlanguage among various formats.
C-Tools can convert the input files between different codes and can generate an input file from a structure
file for a material. The input files can be easily created by clicking the [load] and [save] button, as shown
in Fig.2. Now C-Tools supports the five file formats for DFT codes, xTAPP, OpenMX [4], RSDFT [5],
VASP [6], and Quantum ESPRESSO (PWscf) [7].
Fig.1 TiO2 charge density
by TAPIOCA
Fig.2 an example of creating input files by C-Tools
[1] http://ma.cms-initiative.jp/en/application-list/tapioca.
[2] http://ma.cms-initiative.jp/en/application-list/c-tools.
[3] Yoshihide Yoshimoto, TAPP consortium [email protected].
[4] T. Ozaki, H. Kino, J. Yu, M.J. Han, N. Kobayashi, M. Ohfuti, F. Ishii, T. Ohwaki, H.Weng, Computer
code OpenMX. http://www.openmx-square.org/.
[5] J.-I. Iwata, D. Takahashi, A. Oshiyama, B. Boku, K. Shiraishi, S. Okada, and K. Yabana, J. Comput.
Phys. 229, 2339 (2010).; http://ma.cms-initiative.jp/ja/listapps/rsdft/.
[6] http://www.vasp.at.
[7] http://www.quantum-espresso.org.
P-03
Accurate band structure of wurtzite ZnO calculated with the biorthogonal transcorrelated method
Masayuki Ochi1, Ryotaro Arita2, and Shinji Tsuneyuki3,4
1
Department of Physics, Osaka University, Toyonaka, Osaka 560-0043, Japan
RIKEN Center for Emergent Matter Science (CEMS), Wako, Saitama 351-0198, Japan
3
Department of Physics, The University of Tokyo, Hongo, Bunkyo-ku, Tokyo 113-0033, Japan
4
Institute for Solid State Physics, The University of Tokyo, Kashiwa, Chiba 277-8581, Japan
2
Accurate first-principles electronic structure calculation for strongly correlated
materials has been one of the most challenging and important problems in
computational material science. For this purpose, there have been many attempts to go
beyond the local density approximation (LDA) or the generalized gradient
approximation (GGA), which are standard approximations used in the first-principles
calculations for solids. Recently, wave-function theory has been attracting much
attention because of its great advantage that its accuracy can be systematically improved.
Transcorrelated (TC) method [2-6] is one of the wave function theories and possesses
attractive characteristics: relatively low computational cost, self-interaction free,
independent of density functional theory, self-consistent, etc. In the TC method, manybody Hamiltonian similarity-transformed with the Jastrow factor describes effective
interactions among correlated electrons. Whereas the electronic structure of weakly
correlated materials is well described by the TC method, its accuracy for strongly
correlated solids has not been investigated yet.
In this study, we report the first application of the TC method to 3d transition metal
oxide: ZnO. We adopt the bi-orthogonal formulation of the TC method, BiTC method
[7,8]. Non-Hermitian one-body SCF equation in the (Bi)TC method is solved by
iterative diagonalization using a plane-wave basis set [9]. We find that accuracy of the
band structure is improved by the BiTC method from those obtained with LDA and GW
methods. We will also discuss how the one-body wave functions in the BiTC method
differ from those in other conventional methods.
[1] G. H. Booth, A. Grüneis, G. Kresse, and A. Alavi, Nature 493, 365 (2013).
[2] S. F. Boys and N. C. Handy, Proc. R. Soc. London Ser. A 309, 209 (1969).
[3] S. Ten-no, Chem. Phys. Lett. 330, 169 (2000).
[4] N. Umezawa and S. Tsuneyuki, J. Chem. Phys. 119, 10015 (2003).
[5] R. Sakuma and S. Tsuneyuki, J. Phys. Soc. Jpn. 75, 103705 (2006).
[6] M. Ochi, K. Sodeyama, R. Sakuma, and S. Tsuneyuki, J. Chem. Phys. 136, 094108
(2012).
[7] O. Hino, Y. Tanimura, and S. Ten-no, J. Chem. Phys. 115, 7865 (2001).
[8] M. Ochi and S. Tsuneyuki, Chem. Phys. Lett. 621, 177 (2015).
[9] M. Ochi, Y. Yamamoto, R. Arita, and S. Tsuneyuki, J. Chem. Phys. 144, 104109
(2016).
P-04
Hidden fermionic excitations in strongly-correlated
superconductors
Shiro Sakai
Center for Emergent Matter Science, RIKEN, Wako, Saitama 351-0198, Japan
The dynamics of quasiparticles reflects the pairing mechanism of superconductivity. In
fact, for conventional superconductors, studies on the quasiparticle dynamics played an
essential role in establishing the phonon-mediated pairing mechanism [1]. We study the
quasiparticle dynamics in two different unconventional superconductors: the d-wave
superconducting state in the two-dimensional repulsive Hubbard model [2], and the swave superconducting state in the strongly-attractive Hubbard model in infinite
dimensions [3]. The former is relevant to high-temperature superconductivity in
cuprates while the latter is relevant to the Bose-Einstein condensate observed in
ultracold Fermi gas.
We show that in both cases the quasiparticle dynamics is governed by a coupling to a
hidden fermionic excitation, which generates a pole in self-energy. In the case of
repulsive Hubbard model, this coupling to the hidden fermion strengthens the
superconductivity considerably, being at the origin of the high transition temperature Tc.
The hidden fermion survives even above Tc, yielding a pseudogap in the spectra. The
hidden fermion is a low-energy electronic state emergent due to strong correlations. In
order to characterize and fully identify it, we have investigated how the hidden fermion
behaves as the doping, temperature and the interaction strength change [4].
On the other hand, in the attractive Hubbard model, the hidden fermion traces back to
the excitation present in the atomic limit. In this case, too, the hidden fermion yields the
pseudogap above Tc. However, below Tc, the hidden fermion slightly suppresses the
superconductivity and it loses its intensity as temperature is further lowered.
These results provide us with a unified view on the quasiparticle dynamics in the two
different strongly-correlated superconductors: In both systems, the low-energy
dynamics is governed by a hidden fermionic excitation but of different kind.
[1] W. L. McMillan and J. M. Rowell, Phys. Rev. Lett. 14, 108 (1965).
[2] S. Sakai, M. Civelli, and M. Imada, Phys. Rev. Lett. 116, 057003 (2016).
[3] S. Sakai, M. Civelli, Y. Nomura, and M. Imada, Phys. Rev. B 92, 180503 (R) (2015).
[4] S. Sakai, M. Civelli, and M. Imada, arXiv:1605.05004
P-05
Magnetic phase diagram in hyperkagome iridate Na4Ir3O8
Tomonari Mizoguchi1, Yong-Baek Kim2,3,4
1
Department of Physics, The University of Tokyo, Hongo, Bunkyo-ku, Tokyo 113-0033, Japan
Department of Physics and Centre for Quantum Materials, University of Toronto, Toronto, Ontario
M5S 1A7, Canada
3
Canadian Institute for Advanced Research/Quantum Materials Program, Toronto, Ontario MSG
1Z8, Canada
4
School of Physics, Korea Institute for Advanced Study, Seoul 130-722, Korea
2
Hyperkagome iridate Na4Ir3O8 [1] has attracted a great attention as a candidate
for a spin liquid state. In this material, Ir4+ ions possess the pseudospin jeff=1/2, and they
are on a hyperkagome lattice (i.e., the corner-sharing triangles in three-dimensions),
which is geometrically frustrated. Recently, it has been reported in the μSR [2] and
NMR [3] that this material shows the spin freezing behavior in very low temperature
region.
Motivated by these experiments, we investigated the effect of small anisotropic
spin exchange interactions in addition to a huge antiferromagnetic Heisenberg
interaction [4], since small anisotropic interactions may become important in the low
temperature region. Actually, previous works have shown that selected sets of
anisotropic interactions play an important role in determining the classical ground state
of this material [5-7]. For further understanding of the effect of anisotropic interactions,
the derivation of the generic spin model is highly desirable.
In this presentation, we will first show how to derive a generic spin model by
considering multiorbital interactions and the spin-orbit coupling for t2g orbitals. Then we
will discuss the magnetic phase diagram of that model at the classical level, which is
obtained by a combination of Luttinger-Tisza analysis and classical Monte Carlo
simulated annealing. We find that there are three q=0 states: Z2, Z62p, and Z61p states.
The spin configurations of three q=0 states can be characterized by underlying lattice
symmetries. Finally, we will present the possible explanation for the spin freezing
behavior on the basis of our theoretical analysis.
[1] Y. Okamoto, et al., Phys. Rev. Lett. 99, 137207 (2007).
[2] R. Dally, et al., Phys. Rev. Lett. 113, 247601 (2014).
[3] A. C. Shockley, et al., Phys. Rev. Lett. 115, 047201 (2015).
[4] T. Mizoguchi, et al., arXiv: 1603.00469 (2016).
[5] G. Chen and L. Balents, Phys. Rev. B 78, 094403 (2008).
[6] I. Kimchi and A. Vishwanath, Phys. Rev. B 89, 014414 (2014).
[7] R. Shindou, Phys. Rev. B 93, 094419 (2016).
P-06
“Mott transition” in excitonic system
Fumiya Sekiguchi1,4, Changsu Kim2, Hidefumi Akiyama2, Loren N. Pfeiffer3,
Ken W. West3, Ryo Shimano1,4
1
Department of Physics, The University of Tokyo, Hongo, Bunkyo-ku, Tokyo 113-0033, Japan
2
Institute of Solid State Physics, The University of Tokyo, Kashiwa, 277-8581, Japan
3
Department of Electrical Engineering, Princeton University, New Jersey 08544, USA
4
Cryogenic Research Center, The University of Tokyo, Tokyo, 113-0032, Japan
Mott transition, i.e. the metal-insulator transition (MIT) driven by electron
interactions, has been one of the central problems in condensed matter physics [1].
Among diversity of material systems, an ensemble of excitons, hydrogen-like bound
states of electron-hole pairs, offers an intriguing platform that represents Mott’s original
gedanken experiment on MIT in an array of one-electron atoms [2]. Exciton Mott
transition (EMT) indicates the transition from insulating exciton gas in low density
region to metallic electron-hole (e-h) plasma in high density region. Despite its long
history of investigations, questions about the intrinsic nature of EMT in the low
temperature regime still remain unsettled: 1) whether EMT is a “phase transition” or
crossover? 2) How does it relate to the conventional Mott-Hubbard’s MIT? In this study,
to reach a low temperature limit condition without injecting excess energy to the e-h
system, we resonantly excite high density 1s excitons in bulk GaAs and probed the
dynamics of EMT, especially the temporal evolution of e-h correlation by using THz
spectroscopy. We found that an anomalous metallic phase with peculiar quasiparticle
mass enhancement and scattering rate emerges in the vicinity of Mott transition,
showing a similarity with the non-Fermi liquid phase that emerges on the verge of MIT
in Mott-Hubbard systems. Furthermore, the temporal dynamics after the photoexcitation
suggests that such an anomalous phase is formed through the first-order phase transition.
Mass enhancement and scattering rate extracted from the extended Drude model at the
e-h pair density about three times larger than the Mott density(~ 1.0×1016 cm-3 ), and at
the sample temperature of 5 K.
[1] M. Imada et al, Rev. Mod. Phys. 70, 1039 (1998).
[2] N. F. Mott, Philos. Mag. 6, 287 (1961).
P-07
X-ray magnetic circular dichroism and cluster-model analysis of
the spinel-type vanadate CoV2O4
Yosuke Nonaka1, Goro Shibata1, Rui Koborinai2, Keisuke Ishigami1, Shoya Sakamoto1,
Keisuke Ikeda1, Zhendong Chi1, Tsuneharu Koide3, Arata Tanaka4, Takuro Katsufuji2,
and Atsushi Fujimori1
1
Department of Physics, The University of Tokyo, Hongo, Bunkyo-ku, Tokyo 113-0033, Japan
2
Department of Physics, Waseda University, Tokyo 169-8555, Japan
3
Photon Factory, IMSS, High Energy Accelerator Research Organization, Tsukuba, Ibaraki 3050801, Japan
4
Department of Quantum Matters, ADSM, Hiroshima University, Higashi-Hiroshima 739-8530, Japan
2.0
magnetic moment [ B/atom ]
magnetic moment [ B/atom ]
The spinel-type vanadate AV2O4 has an orbital degree of freedom in the t2g orbitals
of the V3+ ion, and thus the orbital order of V has been intensively studied [1]. Recently,
orbital glass state (short-range orbital order) was found in CoV2O4 below 90K [2, 3].
In order to study details of orbital states in the orbital glass state, we have performed
angle-dependent x-ray magnetic circular dichroism (XMCD) measurements at the BL16A of KEK-PF. In these measurements, we fixed the incident angle of x-rays, and
changed the direction of magnetic field using a ‘vector-type magnet` XMCD apparatus.
The magnetic field of 1 T was applied along the [001] and [111] directions (in the cubic
notation). Spin and orbital magnetic moments deduced using the XMCD sum rules are
shown in Fig. 1, which indicates that the orbital magnetic moments of V are almost
quenched. Figure 2 shows comparison between experiment and cluster-model
calculation. The calculation considering the compressive tetragonal distortion along
[001] direction reproduces experimental spectrum.
Spin
1.5
1.0
0.5
Co
V
30K
70K
110K
0
-0.5
-1.0
[001]
[111]
Magnetic field direction
0.5
Orbital Co
V
30K
70K
110K
0.4
0.3
0.2
0.1
0
[001]
[111]
Magnetic field direction
Fig. 1. Spin and orbital magnetic moments of CoV2O4 at
different temperatures and different magnetic field
directions.
[1] S. -H. Lee et al., J. Phys. Soc. Jpn. 79, 011004 (2010).
[2] R. Koborinai et al., Phys. Rev. Lett. 116, 037201 (2016).
[3] D. Reig-i-Plessis et al., Phys. Rev. B 93, 014437 (2016).
Fig. 2. Comparison
between experiment and
cluster-model calculation
for the V L2,3 edge XMCD.
P-08
Electronic Phase Diagram of Pr1-xLaCexCuO4- as Function of
Electron Number Studied by Angle Resolved Photoemission
Spectroscopy
Dongjoon Song1, H. Eisaki1, and C. Kim2
1Electronics
and Photonics Research Institute, National Institute of Advanced Industrial Science and
Technology (AIST), Tsukuba 305-8568, Japan
2Center for Strongly Correlated Materials Research, Seoul National University, Seoul 08826, Korea
We investigated the evolution of the electronic structure on Pr1-xLaCexCuO4- as a
function of the electron number (n) by means of Angle Resolved Photoemission
Spectroscopy. By employing the Luttinger’s sum rule, we established the relationship
between the superconducting transition temperature (Tc) and n. The renewed phase
diagram possesses a broad superconducting dome with a maximum Tc (Tc,max) at around
n~0.15, which is sharply distinct from the reported ones in which Tc,max is located at the
nominal Ce concentration x~0.10. [1] Besides the increase in the Fermi surface volume,
we observed the systematic change in the pseudo gap (PG) at the antiferromagnetic
(AF) Brillouin zone boundary (hot spot), which is considered as a fingerprint of the
doping dependent AF order. Moreover, we observed the characteristic n dependence of
the nodal gap in the under doped SC samples, which resembles the behaviors of the hole
doped superconductors. [2] In this poster presentation, we present the detailed doping
dependence of these features and discuss their origins, as well as their relation with Tc.
Contact : [email protected]
[1] M. Fujita et al., Phys. Rev. Lett. 101, 107003 (2008).
[2] E. Razzoli et al., Phys. Rev. Lett 110, 047004 (2013).
P-09
Proposal for experimental realization and out-of-order correlation
measurement of the Sachdev-Ye-Kitaev model with ultracold
gases
Ippei Danshita1, Masanori Hanada1,2,3, and Masaki Tezuka4
1Yukawa
Institute for Theoretical Physics, Kyoto University, Kyoto 606-8502, Japan
Institute for Theoretical Physics, Stanford University, Stanford, CA 94305, USA
3The Hakubi Center for Advanced Research, Kyoto University, Kyoto 606-8501, Japan
4Department of Physics, Kyoto University, Kitashirakawa, Kyoto 606-8502, Japan
2Stanford
The Sachdev-Ye-Kitaev (SYK) model [1,2,3], which consists of spin-polarized
fermions with an all-to-all random two-body hopping, has been conjectured to be dual
to a certain quantum gravitational system. We propose [4] that the SYK model can be
engineered by confining ultracold fermionic atoms into optical lattices and coupling two
atoms with molecular states via photo-association lasers. We also explain how to
measure out-of-time-order correlation functions of the SYK model, which allow for
identifying the maximally chaotic property of the black hole.
[1] S. Sachdev, “Bekenstein-Hawking Entropy and Strange Metals”, Phys. Rev. X 5,
041025 (2015)
[2] Talks by A. Kitaev, http://online.kitp.ucsb.edu/online/entangled15/kitaev/ and
http://online.kitp.ucsb.edu/online/entangled15/kitaev2/.
[3] J. Maldacena and D. Stanford, “Comments on the Sachdev-Ye-Kitaev model”,
arXiv:1604.07818 [hep-th] and references therein.
[4] I. Danshita, M. Hanada, and M. Tezuka, “Creating and probing the Sachdev-YeKitaev model with ultracold gases: Towards experimental studies of quantum gravity”,
arXiv:1606.02454 [cond-mat].
P-10
Electronic structure of superconducting parent compound of T’cuprate superconductors Nd2CuO4 studied by hard X-ray
photoemission and soft X-ray absorption spectroscopies
M. Horio1, Y. Krockenberger2, K. Yamamoto3, Y. Yokoyama3, K. Takubo3, Y. Hirata3,
S. Shin3, A. Yasui4, E. Ikenaga4, H. Yamamoto2, H. Wadati3, and A. Fujimori1
1Department
of Physics, The University of Tokyo, Hongo, Bunkyo-ku, Tokyo 113-0033, Japan
Basic Research Laboratories, NTT Corporation, Atsugi, Kanagawa 243-0198, Japan
3
Institute for Solid State Physics, University of Tokyo, Kashiwa, Chiba 277-8561, Japan
4
Japan Synchrotron Radiation Research Institute, Sayo, Hyogo 679-5198, Japan
2NTT
Although doping electrons by substituting Ce4+ for Ln3+ (Ln: rare earth) has long
been considered to be indispensable for the superconductivity in T’-type cuprates,
superconductivity has recently been realized in thin films without Ce substitution only
by post annealing to remove excess oxygen atoms [1,2]. In order to understand the
superconductivity without Ce doping, it is crucial to understand the effect of annealing
on the electronic structure.
For this purpose, we have performed hard X-ray photoemission (HAXPES) and soft
X-ray absorption spectroscopies measurements on thin films of the parent compound of
T’-cuprates Nd2CuO4 with and without annealing. Annealing enhanced a peak  in Cu
2p3/2 HAXPES spectrum (Fig. 1(a)), which originates from core-hole screening by
conduction electrons [3], and the spectral intensity near the Fermi level (Fig. 1(b)),
suggesting dramatic increase of the electrical conductivity by annealing. On the other
hand, Nd 3d5/2 peak shifted toward higher binding energy by 0.22 eV with annealing
(Fig. 1(c)), which was comparable with the chemical-potential shift caused by electron
doping by 15 % [4].
[1] A. Tsukada et al., Solid State Commun. 133, 427 (2005).
[2] Y. Krockenberger et al., Sci. Rep. 3, 2235 (2013).
[3] M. Taguchi et al., Phys. Rev. Lett. 95, 177002 (2005).
[4] N. Harima et al., Phys. Rev. B 64, 220507(R) (2001).
Fig. 1 HAXPES spectra of Nd2CuO4. (a) Cu 2p3/2. (b) Valence band. (c) Nd 3d5/2.
P-11
Superconductivity and Pomeranchuk instability
in two-dimensional repulsive Hubbard model
Motoharu Kitatani1, Naoto Tsuji2, and Hideo Aoki1,3
1
Department of Physics, The University of Tokyo, Hongo, Tokyo 113-0033, Japan
2
RIKEN Center for Emergent Matter Science (CEMS), Wako 351-0198, Japan
3
Electronics and Photonics Research Institute,
Advanced Industrial Science and Technology (AIST), Tsukuba, Ibaraki 305-8568, Japan
Two-dimensional repulsive Hubbard model still harbors fundamental questions, and
challenges elaborate numerical analysis on superconductivity, magnetism and other
instabilities. Here, we employ the combination of the dynamical mean field theory
(DMFT) and the fluctuation exchange (FLEX) approximation in terms of LuttingerWard functional [1,2] to treat the local correlation effect and momentum dependent
pairing interaction simultaneously to explore various instabilities.
First, the result exhibits a superconducting phase with a Tc-dome structure against band
filling, both in the absence and presence of the Fermi surface warping (t '). We have
traced back the origin of the dome to the local vertex correction from DMFT that
renders a filling-dependence in the FLEX self-energy. On top of this, we also find a
phase transition into a Pomeranchuk instability, where the four-fold symmetric Fermi
surface becomes unstable against a spontaneous distortion into two-fold (Fig.), a kind of
electronic nematicity [3,4]. Comparing the superconducting Tc and Pomeranchuk
instability temperature, TcPom, we find TcPom is more sensitive to the Fermi surface
warping. More importantly, if we further study superconductivity with the distorted
Fermi surface, the symmetry of the gap function is slightly changed from ordinary dwave pairing to d+s. We also discuss the effect of this nematicity on superconducting
Tc.
Fig. Spontaneous distortion of the Fermi surface
[1] J. Gukelberger, L. Huang, and P. Werner, Phys. Rev. B 91, 235114 (2015).
[2] M. Kitatani, N. Tsuji and H. Aoki, Phys. Rev. B 92, 085104 (2015).
[3] C. J. Halboth and W. Metzner, Phys. Rev. Lett. 85, 5162 (2000).
[4] H. Yamase and H. Khono, J. Phys. Soc. Jpn. 69, 332 (2000).
P-12
Angle-resolved photoemission study of the electronic structure
in the electronic “nematic” phase of BaFe2As2
K. Koshiishi1, L. Liu1, K. Okazaki1, H. Suzuki1, J. Xu1, M. Horio1,
Y. Nonaka1, H. Kumigashira2, K. Ono2, M. Nakajima3, S. Ishida3,
K. Kihou3, C. H. Lee3, A. Iyo3, H. Eisaki3, S. Uchida1 and A. Fujimori1
1
Department of Physics, University of Tokyo, Tokyo, 113-0033, Japan
Photon Factory, High Energy Accelerator Research Organization, Tsukuba, 305-0801, Japan
3
National Institute of Advanced Industrial Science and Technology, Tsukuba, 305-8568, Japan
2
BaFe2As2, a parent compound of iron-based superconductors, exhibits tetragonal-to-orthorhombic
structural transition at temperature of TS= 142 K, accompanied by stripe-type antiferromagnetic (AFM)
transition. In the antiferromagnetic-orthorhombic phase, electronic nematicity defined as broken
rotational C4 symmetry of electronic structure, has been reported by angle-resolved photoemission
spectroscopy (ARPES) [1] and resistivity measurements [2]. Recently, electronic nematic transition at T*
well above TS has been found by magnetic torque measurement for the parent (T*~170 K) and P-doped
compounds [3]. The investigation of the properties in the electronic nematic phase is expected to give
clues to the mechanism of the superconductivity because the electronic nematic phase is contiguous to the
superconducting dome in phase diagram.
In order to study the band folding caused by antiferro-orbital order predicted for the electronic nematic
phase of BaFe2As2, we have performed ARPES measurements on the temperature dependence of the band
dispersion over a temperature range from 100 K to 200 K on detwinned BaFe2As2. From comparison of
the peak intensity of momentum distribution curves (MDSs) across apices of the Dirac cone which is
feature of reconstructed band structure due to the band folding between different temperatures, one can
see the intensity persists above TS up to ~170 K that consistent with T* defined in Ref. [3]. These results
indicate the existence of an antiferro order which has the same periodicity as the stripe-type AFM
ordering in the electronic nematic phase.
Figure 1. (a) MDC spectra at the binding energy of 20 meV corresponding to the Dirac cone at
various temperatures. (b) Temperature dependence of the peak intensity of the Dirac cone obtained
by integrating MDC curves shown in (a).
[1] M. Yi et al., Proc. Natl. Acad. Sci. U.S.A. 108, 6878 (2011).
[2] S. Ishida et al., Phys. Rev. Lett. 110, 207001 (2013).
[3] S. Kasahara et al., Nature 486, 382 (2012).
P-13
Nonlinear optical response in electron-phonon coupled
superconductors: Effects of Higgs amplitude mode
Naoto Tsuji1, Yuta Murakami2,3, and Hideo Aoki2,4
1
RIKEN Center for Emergent Matter Science (CEMS), Wako 351-0198, Japan
Department of Physics, University of Tokyo, Hongo, Bunkyo-ku, Tokyo 113-0033, Japan
3
Department of Physics, University of Fribourg, 1700 Fribourg, Switzerland
4
Electronics and Photonics Research Institute, Advanced Industrial Science and Technology (AIST),
Umezono, Tsukuba, Ibaraki 305-8568, Japan
2
Higgs amplitude mode is a collective mode in superconductors corresponding to the
coherent amplitude oscillation of the superfluid density, which plays an important role
in nonequilibrium low-energy dynamics of superconductors. In recent terahertz pumpprobe experiments [1][2], it has been shown that the Higgs mode can be generated by
irradiation of laser fields. Along with this, it has been demonstrated [2] that thirdharmonic generation (THG) can be resonantly enhanced when the doubled frequency
(2) of the laser coincides with the superconducting gap (2), which is nothing but the
energy of the Higgs mode. On the other hand, at the same energy lie individual
excitations of Cooper pair breaking or density fluctuations, which poses a question of to
what extent these two contribute to the THG resonance. The BCS theory predicts that
the THG signal is dominated by the pair breaking if a general lattice with a general
polarization of the laser field is taken. On the other hand, dynamical correlation effects
such as the strong electron-phonon coupling allows for the resonant coupling between
the light and Higgs mode, which is ignored in the BCS approximation.
Motivated by this, in the present study we investigate the nonlinear optical response
in electron-phonon coupled superconductors beyond the BCS approximation using the
dynamical mean-field theory (DMFT) [3]. To evaluate the dynamical vertex correction,
we formulate a novel approach we call the “dotted DMFT”, which enables us to
determine the vertex correction without explicitly solving the Bethe-Salpeter equation
and analytical continuation. We apply the method to the Holstein model, a typical
model for electrons interacting with phonons. We find that the Higgs-mode contribution
to the THG intensity is in fact enhanced up to a comparable order of magnitude to the
pair breaking contribution due to a retardation effect via the electron-phonon coupling.
This implies a possibility that the effects neglected in the BCS approximation
significantly contribute to nonlinear optical responses of superconductors.
[1] R. Matsunaga, Y. I. Hamada, K. Makise, Y. Uzawa, H. Terai, Z. Wang, and R.
Shimano, Phys. Rev. Lett. 111, 057002 (2013).
[2] R. Matsunaga, N. Tsuji, H. Fujita, A. Sugioka, K. Makise, Y. Uzawa, H. Terai, Z.
Wang, H. Aoki, and R. Shimano, Science 345, 1145 (2014).
[3] N. Tsuji, Y. Murakami, and H. Aoki, in preparation.
P-14
A new method for calculating the one-electron energy spectrum
of huge systems based on the divide-and-conquer DFT method
Shunsuke Yamada1, Ryosuke Akashi2, and Shinji Tsuneyuki1,2
1
Department of Physics, The University of Tokyo, Hongo, Bunkyo-ku, Tokyo 113-0033, Japan
Institute for Solid State Physics, The University of Tokyo, Kashiwa, Chiba 277-8581, Japan
2
Linearly scaling methods for ab initio electron structure calculations for huge systems
have been widely pursued by various groups. The previous methods mostly focus only
on the total energy, the electron density and the forces of the systems, and cannot yield
the one-electron energy spectrum. Some exceptions are applicable to only specific
systems such as covalent bond molecules [1].
We develop a new method for calculating the spectrum and orbitals of general
large-scale systems based on Lean Divide-and-Conquer DFT (LDC-DFT) method [2],
which is accurate and versatile divide-and-conquer method for density functional theory.
In LDC-DFT, a large system is divided into small fragments and the density of the
whole system can be easily obtained by patching the fragment densities. For the
spectrum calculation, we reuse the fragment orbitals used for this density evaluation.
The one-electron Hamiltonian matrix of the whole system is represented with the
fragment orbitals as a basis set. The orbital of the whole system is thus represented by a
linear combination of the fragment orbitals. As a consequence, this new method yields
fast and accurate description of the energy spectrum and orbitals of general huge
systems.
Remarkably, the present method enables us to implement an efficient algorithm
for the calculation with the exact exchange. The Hamiltonian of a gapped system can be
approximately divided in the LDC-DFT manner because of near-locality of the exact
exchange potential [3,4]. We showed that the spectra of bulk Si and GaAs/AlAs
superlattice with PBE0 hybrid functional are obtained through our method.
[1] S. Tsuneyuki et al., Chem. Phys. Lett. 476, 104 (2009).
[2] F. Shimojo et al., J. Chem. Phys. 140, 18A529 (2014).
[3] W. Kohn, Phys. Rev. Lett. 76, 3168 (1996).
[4] E. Prodan and W. Kohn, Proc. Natl. Acad. Sci. U.S.A. 102, 11635 (2005).
P-15
Ab-initio study on transition-metal-doped Nd-Fe-B magnets
Yasutomi Tatetsu1, Shinji Tsuneyuki2, and Yoshihiro Gohda1,3
1
Department of Physics, The University of Tokyo, Hongo, Bunkyo-ku, Tokyo 113-0033, Japan
Institute for Solid State Physics, The University of Tokyo, Kashiwa, Chiba 277-8581, Japan
3
Department of Materials Science and Engineering, Tokyo Institute of Technology, Yokohama,
Kanagawa 226-8502, Japan
2
Nd-Fe-B sintered magnets are widely used in many applications because of having a
high energy product (BH)max compared to other permanent magnets. However, the
thermal instability of their coercivity at high temperatures is a crucial problem and the
mechanism for the low coercivity is unclear yet. As reported in several experimental
studies [1-3], doping the small amount of light elements, for example Ni, Cu, Zn, and
Ga, into Nd-Fe-B magntes works effectively in order to increase the coercivity. These
elements contribute to improving the coercivity of Nd-Fe-B magnets and are thought to
be around the grain boundary between main grains Nd2Fe14B and subphases.
Nevertheless, the mechanism of how these elements improve the coercivity is not clear
and there is no guiding principle in which elements can improve the coercivity.
We have studied magnetic and electronic properties of transition-metal (TM) -doped
Nd2Fe14B bulk and slab systems, where TM = Al, Si, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn,
Ga, Ge, from first-principles calculations in order to understand which elements can
improve the magnetic anisotropy K1 of Nd. We used the computational code OpenMX
[4] which is based on optimized pseudopotentials and pseudo-atomic-orbital bases
functions within density functional theory. We chose an open-core pseudopotential for
Nd atoms in which well-localized 4f electrons are treated as spin-polarized core
electrons. The generalized gradient approximation (GGA) was used as the PerdewBurke-Ernzerhof (PBE) exchange-correlation functional [5]. By analysing the formation
energies in these systems, we find that the Fe 4c site at the surface is easily replaced by
many of TM atoms. Furthermore, we calculated the magnetic anisotropy of Nd which is
strongly related to the coercivity of Nd-Fe-B magnets. By considering the formation
energy and the improvement of K1, we concluded that doping Ni, Cu, Zn, and Ga at the
Fe 4c site is one of the keys to improve K1 of Nd.
[1] H. Sepehri-Amin et al., Acta Mater. 61, 6622 (2013).
[2] C. D. Fuerst and E. G. Brewer, App. Phys. Lett. 56, 2252 (1990).
[3] T. Sasaki et al., Scripta Materialia 133, 218 (2016).
[4] http://www.openmx-square.org.
[5] J. P. Perdew, K. Burke, and M. Ernzerhof, Phys. Rev. Lett. 78, 1396 (1997).
P-16
-pairing superconductivity in
periodically-driven attractive Hubbard model
Sota Kitamura1 and Hideo Aoki1,2
1
Department of Physics, The University of Tokyo, Hongo, Tokyo 113-0033, Japan
Electronics and Photonics Research Institute, Advanced Industrial Science and Technology (AIST),
Tsukuba, Ibaraki 305-8568, Japan
2
A novel possibility of a dynamical phase transition from an ordinary s-wave
superconductor into an exotic pairing is theoretically explored by periodically driving
the system. Namely, we propose for the attractive Hubbard model that the pairing
symmetry can be changed in an AC field to an “-pairing” [1], where each Cooper pair
has a nonzero total momentum (π,π,...).
In the large-U attractive Hubbard model, fermions form pairs in real space and
behave like a bosonic s-wave superfluid. We then incorporate the effect of the AC drive
by deriving a Floquet effective Hamiltonian on a coarse-grained time scale with faster
time evolution renormalized.
We find that the obtained model for bosonic pairs has pair-hopping (J) and pair-pair
interaction strengths drastically different from those in equilibrium. In particular, one
can invert the sign of the pair-hopping J (see Fig. below), which is expected to lead to
the -pairing superconductivity, since the band structure of bosonic pairs now has a
bottom at (π,π,...).
We then devise a way to realize this in cold atoms on optical lattices. Cold-atom
systems are regarded as ideal isolated systems where dissipation is absent, so that a
sudden flipping of the band structure will not simply result in a dynamical phase
transition. However, we can propose a protocol for inducing a transition to a desired
destination even in isolated systems, by a stepwise change of amplitude [2]. There we
utilize the fact that the attractive Hubbard model has dynamical instabilities between
superconductivity and charge-order phases, from which one can induce the -pairing
superconductivity via the dynamically induced charge-ordered phase.
[1] C. N. Yang, Phys. Rev. Lett. 63, 2144 (1989).
[2] S. Kitamura and H. Aoki, arXiv:1511.07890.
Fig.: Schematic picture of the ground states
in ordinary bands (left) and flipped bands (right).
P-17
First-principles prediction of perovskite-type oxyhydrides
ATiO2H (A = K, Rb, Cs) with a two-dimensional electronic state
Nobuya Sato1, Ryosuke Akashi1, and Shinji Tsuneyuki1,2
1
Department of Physics, The University of Tokyo, Hongo, Bunkyo-ku, Tokyo 113-0033, Japan
The Institute for Solid State Physics, The University of Tokyo, Kashiwanoha, Kashiwa-shi, Chiba
277-8581, Japan
2
Perovskite-type oxides ABO3 have been used for
ferroelectric and piezoelectric devices and widely studied to
improve their functionality. Though their ferroelectricity
K
and piezoelectricity are controlled by partially substituting
Ti
atoms, possible combinations of atoms are limited to satisfy
O
the charge neutrality, e.g. A2+(B,B')4+O2−3. If it is possible to
H
substitute oxygen atoms with monovalent anions X−, more
varieties of compounds such as A+B4+O2−2X− could be
realized, and in recent years, such substitution actually
performed for fluorine anions [1]. More recently,
substitution with hydrogen anions (H−) has become Fig. 1. The crystal structure
available [2,3]. Since the orbital character of hydrogen of KTiO2H.
atoms (1s) is different from that of oxygen atoms and fluorine atoms (2s and 2p),
compounds A+B4+O2−2H− might have novel electronic properties.
To explore such possibilities, we perform first-principles calculations of KTiO2H [4].
We found a stable perovskite-type structure as depicted in Fig. 1. Its formation energies
for possible synthesis reactions are negative. Its electric polarization of 101 μC/cm2 is
comparable to that of PbTiO3. Remarkably, the valence-band top state has significant
two-dimensional character as shown in Fig. 2. This state is characterized by in-plane O
2p and H 1s states. In KTiO2F, this state is hidden deep in other valence-band states,
which indicates that this two-dimensional hole
state originates from the electron affinity of
hydrogen atoms and the symmetry of the 1s
orbital. Furthermore, we study RbTiO2H and
CsTiO2H. Their crystal and electronic structures
are quite similar to those of KTiO2H, respectively,
implying robust existence of the two-dimensional Fig. 2. The band structure of KTiO2H.
state for the series of MTiO2H against The two-dimensional state is at Y–T.
The valence band maximum is set to be
substitution of monovalent cation M+.
zero.
[1]
[2]
[3]
[4]
T. Katsumata, H. Umemoto, Y. Inaguma, et al., J. Appl. Phys. 104, 044101 (2008).
Y. Kobayashi, O. J. Hernandez, T. Sakaguchi, et al., Nature Mater. 11, 507 (2012).
T. Yajima, A. Kitada, Y. Kobayashi, et al., J. Am. Chem. Soc. 134, 8782 (2012).
N. Sato and S. Tsuneyuki, in preparation.
P-18
Magnéli-type phases as the missing link of
the low-Tc—high-Tc superconducting phases in compressed
sulfur hydride
Ryosuke Akashi1, Mitsuaki Kawamura2, Wataru Sano3,4, Yusuke Nomura3,4,
Ryotaro Arita4,5 and Shinji Tsuneyuki1,2
1Dept.
Phys., The University of Tokyo, Hongo, Bunkyo-ku, Tokyo 113-0033, Japan
2ISSP, The University of Tokyo, Kashiwa, Chiba 277-8581, Japan
3Dept. Appl. Phys., The University of Tokyo, Hongo, Bunkyo-ku, Tokyo 113-8656, Japan
4
RIKEN Center for Emergent Matter Science, Wako, Saitama 351-0198, Japan
5
JST-ERATO, AIMR, Tohoku University, Sendai, Miyagi 980-8577, Japan
The discovery of high temperature superconductivity in compressed sulfur
hydride [1] has a tremendous impact on the scientific community. In contrast to
other high-Tc superconducting materials such as cuprate, the dominant
superconducting mechanism has been acknowledged to be the conventional
phonon-mediated one. Various studies including ours [2] have aimed at the
reproduction of the experimentally observed values of Tc from the first-principles.
Theoretically predicted structures such as P-1-H2S [3], P1-H5S2 [4] and Im-3m H3S
[5] structures have been shown to yield the Tc values close to the experimentally
observed low and high Tc s, respectively. Although the end points of the low-Tc—
high-Tc phase transformation are thus being clarified, the transition path between
them has remained an unsolved problem. When the system is compressed at
moderately low temperatures, the experimentally observed values of Tc show
continuous but steep increase toward the high-Tc phase [1], suggesting an
emergence of peculiar intermediate phases linking the low- and high-Tc phases.
However, first-principles reproduction of this behavior has yet been unprecedented,
despite accumulated proposals of candidate crystal structures.
We propose a solution to the problem of intermediated phases [6]. Namely, we
report a “Magnéli”-type infinite sequence of metastable crystal structures having
intermediate compositions HxS (2<x<3). The newly found structures are long-period
modulated crystals where slab-like H2S and H3S regions intergrow in a microscopic
scale. Structures with slightly different compositions are constructed by local
formation of the H3S slab in the H2S regions. We demonstrate that the gradual
transformation through the local H3S-slab formation well reproduces the
experimentally observed steep increase of Tc.
[1] A. P. Drozdov, M. I. Eremets, and I. A. Troyan, V. Ksenofontov, and S. I. Shylin,
Nature (London) 525, 73 (2015).
[2] RA, M. Kawamura, S. Tsuneyuki, Y. Nomura, R. Arita, Phys. Rev. B 91, 224513
(2015).
[3] Y. Li et al., J. Chem. Phys. 140, 174712 (2014).
[4] T. Ishikawa et al., Sci. Rep. 6, 23160 (2016).
[5] D. Duan et al., Sci. Rep. 4, 6968 (2014).
[6] RA, W. Sano, R. Arita, S. Tsuneyuki, arXiv:1512.06680.
P-19
RISB study on f2-configuration quasiparticle systems
Taichi Hinokihara1, Atsushi Tsuruta2, and Kazumasa Miyake3
1
Department of Physics, The University of Tokyo, Hongo, Bunkyo-ku, Tokyo 113-0033, Japan
Division of Materials Physics, Department of Materials Engineering Science, Graduate School of
Engineering Science, Osaka University, Toyonaka, Osaka 560-8531, Japan
3
Toyota Physical and Chemical Research Institute, Nagakute, Aichi 480-1192, Japan
2
Some uranium and praseodymium heavy electron systems show unconventional
behaviors which cannot be explained by Doniach’s phase diagram. It is assumed that
two electrons on well-localized f-orbitals (f2-configuration system) play an important
role as the origin of the unconventional phenomena because of its variety of localized
states owing to out of the Kramers theorem. Especially, UPt3 and UBe13 provide us
attractive phase diagrams that include heavy Fermi liquid, non-Fermi liquid and
unconventional superconductivity. However, few theoretical works have made based on
the multi-orbital periodic Anderson model with crystalline electric field (CEF) effect [1].
Hence, simple theoretical method that can be widely applied to complicated model is
needed for analyzing f2-configuration heavy quasiparticle system.
In this presentation, we focus on the relation between heavy quasiparticle state and
non-Kramers singlet ground state systems: Γ1 ground state system in cubic symmetry,
which is possible for UBe13; and Γ4 ground state system in hexagonal symmetry for
UPt3. We evaluate three-orbital periodic Anderson model with CEF effect by means of
the rotationally invariant slave boson (RISB) formalism in saddle point approximation
[2].
In the case of Γ1 ground state system, a first-order transition line appears between
CEF singlet ground state (localized f-electron) and Femi liquid (itinerant f-electron). In
both phases, all f-orbitals do not renormalized to be a heavy quasiparticle
On the contrary, Γ4 ground state system shows not first-order transition but the
anomalous heavy quasiparticle behavior that is insensitive to magnetic field. This result
is consistent with the quasiparticle behavior on UPt3.
In this presentation, we report results for Γ1 system and Γ4 system and discuss the
origin of the different behaviors.
[1] H. Ikeda and K. Miyake: J. Phys. Soc. Jpn. 66 3714 (1997)
[2] F. Lechermann, A. Georges, G. Kotliar, and O. Parcollet: Phys. Rev. B 76, 155102
(20007)
P-20
Direct Observation of Micro Structure on the
Superconducting Single Crystals of KxFe2-ySe2
Masashi Tanaka1, Yusuke Yanagisawa1,2, Hiroyuki Takeya1, and Yoshihiko Takano1,2
1
MANA, National Institute for Materials Science, 1-2-1 Sengen, Tsukuba, Ibaraki 305-0047,
Japan
2
University of Tsukuba, 1-1-1 Tennodai, Tsukuba, Ibaraki305-8577, Japan
Layer structured iron selenide, FeSe has the simplest crystal structures among
iron-based superconductors. It shows superconductivity with transition temperature (Tc)
around ~10 K under ambient pressure. The Tc increases up to 37 K by applying high
pressure [1-3]. When potassium is intercalated between FeSe layers, the Tc increases
above 30 K. It has been reported as potential superconductors with Tc’s of 30-48 K.
However, there is no clear answer to identify the relationship between the surface
morphology, compositional ratio and its crystal structure, mainly due to its intrinsic phase
separation.
In this study, we directly reveal the correspondence among them in the single
crystals with Tc onset around 44 K with TEM measurements supported by a microsampling technique. Island-like parts on the surface of the crystals clearly show
diffraction spots identical to those of the Fe-vacancy-disordered phase without Fe defects.
It is related to the KxFe2Se2 having a perfect FeSe layers resulting in the appearance of
higher Tc onset of 44 K. The generation of the higher Tc phase is assisted by the formation
of the carrier doped Fe-vacancy-ordered phase, which shows zero resistivity at ~33 K.
The appearance of superconductivity in K-Fe-Se system is discussed on the basis of the
measurements and in-situ X-ray diffraction study [4, 5].
References
[1] Y. Mizuguchi et al., Appl. Phys. Lett. 93, 152505 (2008).
[2] S. Margadonna et al., Phys. Rev. B 80, 064506 (2009).
[3] S. Masaki et al., J. Phys. Soc. Jpn. 78, 063704 (2009).
[4] M. Tanaka et al. J. Phys. Soc. Jpn. 85, 044710 (2016).
[5] M. Tanaka et al. Arxiv.
P-21
Two-Particle Self-Consistent Analysis for the Electron-Hole
Doping Asymmetry of Superconductivity in High-Tc Cuprates
Daisuke Ogura, and Kazuhiko Kuroki
Department of Physics, Graduate School of Science, Osaka University, 1-1 Machikaneyama,
Toyonaka, Osaka 560-0043, Japan
Despite the long history, there still remain various unsolved problems in the study of
the high-Tc cuprate superconductors. The striking electron-hole asymmetry in the
doping dependence of the superconducting transition temperature Tc between the holeand electron-doped compounds is among those unsolved problems. It is well-known
that in the hole-doped systems, Tc exhibits a dome-like feature against the doping rate,
namely, Tc first increases upon doping, then yields a maximum value, and finally turns
to decrease with further doping. On the other hand, recent experiments reveal that Tc in
the electron-doped systems, monotonically increases as the doping is reduced, at least
down to a very small doping rate [1-4].
To understand the origin of this electron-hole asymmetry of Tc, we study the threeband d-p model that explicitly considers the in-plane oxygen 2px, y orbitals in addition to
the copper 3dx2-y2 orbital. To treat the correlation effect effectively, we apply the TwoParticle Self-Consistent method [5, 6], in which the vertex corrections are considered in a
non-perturbative manner for a virtually infinite system. Also to perform realistic
calculations, we construct the effective tight-binding model from the first-principles
band calculation using the maximally localized Wannier basis [7, 8]. We evaluate the
doping dependence of the linearized Eliashberg equation for d-wave pairing, which is a
measure of Tc. The obtained doping dependence reproduces the asymmetric behavior of
Tc. This is explained as a combined effect of the intrinsic electron-hole asymmetry in
systems comprising Cu3d and O2p orbitals and band-filling-dependent vertex correction.
[1] A. Tsukada, et al., Solid State Commun. 133,427 (2005).
[2] M. Brinkmann, et al., Phys. Rev. Lett. 74, 4927 (1995).
[3] Y. Krockenberger, et al., Sci. Rep. 3, 2235 (2013).
[4] T. Adachi, et al., J. Phys. Soc. Jpn. 82, 063713 (2013).
[5] Y. Vilk and A.-M. Tremblay, J. Phys. I (France) 7, 1309 (1997).
[6] H. Miyahara, et al, Phys. Rev. B 87, 045113(2013).
[7] A. A. Mostofi, et al., Phys. Commun. 178, 685 (2008).
[8] J. Kunes, et al., Comput. Phys. Commun. 181, 1888 (2010).
[9] D. Ogura, and K. Kuroki, Phys. Rev. B 93, 144511 (2015).
P-22
Nonthermal crystal-to-amorphous transition of Ge2Sb2Te5 by
irradiating ultrashort pulse laser
Yuta Tanaka1 and Shinji Tsuneyuki1,2
1
Department of Physics, The University of Tokyo, Hongo, Bunkyo-ku, Tokyo 113-0033, Japan
Institute for Solid State Physics, The University of Tokyo, Kashiwa-no-ha, Kashiwa, Chiba 2770882, Japan
2
Chalcogenide phase change materials (PCM) are used in rewritable optical discs,
such as DVD-RAM and Blu-ray Disc. These devices exploit fast and reversible phase
transition of the PCM between amorphous and crystalline phases, which is caused via
thermal process by irradiating long-duration laser. Recently, ultrafast crystalline-toamorphous phase transition by irradiating ultrashort pulse laser has been proposed [1],
which is called nonthermal amorphization. The purpose of our study is to reveal atomic
dynamics of this nonthermal amorphization in the PCM from first principles to realize
ultrafast memory encoding.
In this work, we study Ge2Sb2Te5 (GST), which exhibits the best performance
among the PCM. To describe the nonthermal process, we assumed that electron
distribution reaches the Fermi-Dirac distribution shortly after ultrashort pulse laser
irradiation, and adopted a two-temperature model, in which the temperature of the
electron subsystem is very high while that of the atomic subsystem remains low. Since
GST intrinsically contains a certain amount of defects, first we calculated total-energy
of several defect distributions to investigate the most probable ones. It was found that
the structures which have planar intrinsic defects in the {111} planes are generally more
stable than those with disordered defect distribution. However, the energy difference
between these structures is about 30 meV/atom, so we consider that both structures
might coexist. Next, we carried out ab initio molecular dynamics calculation at finite
temperature. As a result, when electronic temperature is 1.25 eV, the structures which
have disordered defect distribution
became
amorphous
via
highly
coordinated structure (Fig. 1). The
atomic dynamics shown by our result is
different from one suggested in Umbrella
flip model [2], which is the most famous
model
explaining
nonthermal
amorphization of GST. Based on our
calculation results, we suggest a new
nonthermal amorphization model.
[1] J. Siegel et al., J. Appl. Phys. 103, 023516 (2008).
[2] V. Kolobov et al., Nat. Mat. 3, 703 (2004).
P-23
Topological Excitations in Frustrated Magnets
Yutaka Akagi1, Hiroaki T. Ueda2, and Nic Shannon3
1
Department of Physics, The University of Tokyo, Hongo, Bunkyo-ku, Tokyo 113-0033, Japan
2
Faculty of Engineering, Toyama Prefectural University, Izumi 939-0398, Japan
3
Okinawa Institute of Science and Technology Graduate University, Okinawa 904-0495, Japan
Topological excitations play an important role in both conventional liquid crystals,
such as the nematic phase, and in the theory of two-dimensional quantum spin liquids
[1]. However, relatively little is known about their role in the magnetic analogue of a
liquid crystal the “quantum spin-nematic”, a phase which breaks spin-rotation
symmetry without breaking time-reversal symmetry. Moreover, most studies on such
topological excitations were carried out in the continuum limit [2-5]. Little is also
known about the properties of topological excitations in microscopic lattice models.
Then, we investigate such topological excitations in these nontrivial states in a
microscopic model. The model which we consider is the spin-1 bilinear biquadratic
model on the triangular lattice, which is known to support a number of nontrivial
magnetic states [6-8]. Using homotopy analysis and numerical minimization of a
variational wave function, we exhaustively examine what topological defects are in this
model.
(1) We identify a new family of solitons at special SU(3) symmetric point. We also find
that a soliton with higher topological charge spontaneously decays into “elementary”
solitons with emergent interaction [9,10].
(2) In antiferro nematic phase with SU(2) symmetry [3-5], we find that C0 type point
defect spontaneously splits into two Cz type point defects, expanding the vortex core
region [10].
(3) In antiferromagnetic 120° order, we clarify that the famous Z2 vortex [11] has a
preference of orientation in this model. As a nontrivial result, we also find the spin
lengths are diminished near vortex core, depending on parameter region [10].
[1] A. V. Chubukov, S. Sachdev, and T. Senthil, Nucl. Phys. B 426 [FS], 601 (1994).
[2] B. A. Ivanov, R. S. Khymyn, and A. K. Kolezhuk, Phys. Rev. Lett. 100, 047203
(2008).
[3] T. Grover and T. Senthil, Phys. Rev. Lett. 107, 077203 (2011).
[4] J. Takano and H. Tsunetsugu, J. Phys. Soc. Jpn. 80, 094707 (2011).
[5] C. Xu and A. W. W. Ludwig, Phys. Rev. Lett, 108, 047202 (2012).
[6] A. Lauchil, F. Mila, and K. Penc, Phys. Rev. Lett. 97, 087205 (2006).
[7] H. Tsunetsugu and M. Arikawa, J. Phys. Soc. Jpn. 75, 083701 (2006).
[8] A. Smerald and N. Shannon, Phys. Rev. B 88, 184430 (2013).
[9] H. T. Ueda, Y. Akagi, and N. Shannon, Phys. Rev. A. 93, 021606(R) (2016).
[10] Y. Akagi, H. T. Ueda, and N. Shannon, in preparation.
[11] H. Kawamura and S. Miyashita, J. Phys. Soc. Jpn. 53, 4138 (1984).
P-24
The Triexciton Stabilization in Indirect Gap Semiconductors
Hiroki Katow1, Junko Usukura2, Ryosuke Akashi1, Kálmán Varga3, and Shinji
Tsuneyuki1
1
Department of Physics, The University of Tokyo, Hongo, Bunkyo-ku, Tokyo 113-0033, Japan
Department of Physics, Tokyo University of Science, 1-3 Kagurazaka, Tokyo 162-8601, Japan
3
Department of Physics and Astronomy, Vanderbilt University, Nashville, Tennessee 37235, United
States
2
There are a wide variety of electron-hole bound states in photo-excited semiconductors
due to the attractive or repulsive Coulomb interaction between carriers. Fundamental
composite particles are the exciton, trion, and biexciton. The polyexciton, excitonic Nbody complexes are considered to be one of such various electron-hole many-body
bound states. These bound states have great significance since they play dominant role
in the optical processes of solids, and they are also attracting fundamental interests as
part of electron-hole many-body phases. Although there have been some theoretical
studies up to charged biexciton in bulk systems [1], numerical investigations for PEn (n
> 2) are scarce in bulk systems.
It is not an easy task to show the stability of PEn for n > 2, or in general, complex
particles in general unit charge systems. For example, Positronium trimer (Ps3) was
shown not to be stable by a precise numerical calculation [2], and the Hydrogen trimer
(H3) is also known to be unstable [3]. This fact suggests that PEn (n > 2) should not be
stable bound state inside direct gap semiconductors. However, in the case of indirect
gap semiconductors, it has been predicted that degenerate valleys and valence bands
relax the Pauli repulsion between identical particles and make PEn stable [3]. Recently,
Omachi et al. [4] reported experimental observation of 6 photoemission peaks
energetically lower than the single exciton peak in diamond. They attributed these peaks
to exciton decay inside PEn (n = 2-6). Here, the peak precision was high thanks to the
large exciton binding energy in diamond, and it became possible to compare the
theoretically calculated values with the experimentally observed values.
Numerical simulation of an electron-hole system with more than 6 particles is a
challenging task. It would be mainly due to the high computational cost of solving fewbody systems with more than 6 particles, complexities of degenerate valley and band,
and the large effective mass anisotropy. We employed the explicitly correlated Gaussian
(ECG) basis for the trial wave function which enables us to calculate the Hamiltonian
analytically. In this presentation, we report the first numerical evidences for ground
state excitonic complexes in diamond up to the triexciton with anisotropic effective
masses and degenerate valley and band degree of freedoms by direct calculation of
quantum few-body system.
[1] J. Usukura, Y. Suzuki, and K. Varga, Phys. Rev. B, 59, 5652(1999).
[2] S. Bubin, O. V. Prezhdo, and K. Varga, Phys. Rev. A, 87, 054501(2013).
[3] G. Calzaferri, Chem. Phys. Lett., 87, 443(1982).
[4] J. Shy-Yih Wang and C. Kittel, Phys. Lett. 42A, 189(1972).
[5] J. Omachi et al., Phys. Rev. Lett. 111, 026402(2013)
Program
Day 1 (Saturday, June 18th, 2016)
13:30 - 13:35
Opening
Session I (Chair: H. Aoki)
13:35 - 14:20
F. Duncan M. Haldane (Princeton Univ.)
Composite bosons and fermions in a partially-filled Landau Level
14:20 - 15:05
Ryo Shimano (Univ. Tokyo)
Study of nonequilibrium responses in quantum matter - from QHE to
superconductor
15:05 - 15:50
Koji Hashimoto (Osaka Univ.)
Gravity challenges strongly correlated matter: Non-equilibrium phase diagram
15:50 - 16:10
Coffee Break
Session II (Chair: K. Held)
16:10 - 16:55
Hirosi Ooguri (Caltech & Kavli IPMU)
Gravitational Positive Energy Theorems from Information Inequalities
16:55 - 17:40
Hideo Aoki (Univ. Tokyo & AIST)
Perspective of superconductivity, topology and nonequilibrium
18:30 -
Banquet at Tokyo Kaikan Level XXI
Day 2 (Sunday, June 19th, 2016)
Session III (Chair: P. Werner)
9:00 - 9:45
Piotr Maksym (Univ. Leicester & Univ. Tokyo)
Graphene in External Potentials: Links with Atomic Physics and Optics
9:45 - 10:30
Yoshiro Takahashi (Kyoto Univ.)
Quantum simulation using ultracold atoms in an optical lattice
10:30 - 10:50
Coffee Break
10:50 - 11:35
Karsten Held (TU Wien)
Oxide heterostructures: from efficient solar cells to spin-orbit coupling
11:35 - 12:20
Jun Akimitsu (Okayama Univ. & Hiroshima Univ.)
Quo Vadis Superconductivity?
12:20 - 14:20
Lunch Break
12:20 - 14:20
Poster Session
Session IV (Chair: S. Tsuneyuki)
14:20 - 15:05
Ryotaro Arita (RIKEN CEMS)
High temperature superconductivity in light element materials
15:05 - 15:50
Philipp Werner (Univ. Fribourg)
Hund coupling effects in multi-orbital Hubbard systems
15:50 - 16:35
Kazuhiko Kuroki (Osaka Univ.)
Optimization of unconventional superconductivity through electron correlation
designing
16:35 -
Closing