What's New

2020

The "Floquet topological insulator", which was theoretically predicted by Takashi Oka and Hideo Aoki [Phys. Rev. B 79, 081406(R) (2009)] to occur in graphene when illuminated by a circularly-polarised light, is now experimentally detected by James McIver et al of the Max-Planck-Institut Hamburg, and published in Nature Physics 16, 38 (2020), featured on its cover.
Partially flat band systems are shown to accommodate unconventional superconductivity in peculiar ways by Sharareh Sayyad, Edwin W. Huang, Motoharu Kitatani, Mohammad-Sadegh Vaezi, Zohar Nussinov, Abolhassan Vaezi and Hideo Aoki: Pairing and non-Fermi liquid behavior in partially flat-band systems, as published in Phys. Rev. B 101, 014501 (2020).

2018

Higgs mode in a high-Tc cuprate with a d-wave pairing is now detected experimentally by Ryo Shimano's group (Univ. of Tokyo), where Aoki and Naoto Tsuji (Riken) have contributed theoretically. The paper is now published in Phys. Rev. Lett. as an editor's suggestion. [Kota Katsumi, Naoto Tsuji, Yuki I. Hamada, Ryusuke Matsunaga, John Schneeloch, Ruidan D. Zhong, Genda D. Gu, Hideo Aoki, Yann Gallais, Ryo Shimano: Higgs mode in the d-wave superconductor Bi2Sr2CaCu2O8+x driven by an intense terahertz pulse, Phys. Rev. Lett. 120, 117001 (2018)]

2017

Aoki is taking a position of guest professorship at ETH Zurich (Department of Physics) for Sept - Dec 2017. He is giving lectures on "Quantum states of matter" in the graduate course.

2016

"International Symposium on New Horizons in Condensed Matter Physics"
(Sat 18 - Sun 19 June 2016)
will be held at Koshiba Hall, University of Tokyo (Hongo campus). Aoki is joining the organising committee, with Prof. Tsuneyuki as the chair.
http://fpmrt.riken.jp/public_html/aoki.symposium/index.html
Confirmed invited speakers include Jun Akimitsu, Hideo Aoki, Ryotaro Arita, F. D. M. Haldane, Koji Hashimoto, Karsten Held, Kazuhiko Kuroki, Hiroshi Ooguri, Ryo Shimano, Yoshiro Takahashi , Philipp Werner.
Prof. Hideo Aoki is retiring from the Department of Physics, University of Tokyo in March 2016 at the age of 65. He is giving a final lecture entitled
"Renaissance in the condensed-matter physics --- superconductivity, topological systems and no nequilibrium"
in Koshiba Hall on 10 March 2016.
Contents

2015

Prof. Hideo Aoki has retired from the Department of Physics, University of Tokyo in March 2016. He continues his research with external funds at

Department of Physics,
University of Tokyo,
Hongo, Tokyo 113-0033, Japan

and at

Electronics and Photonics Research Institute,
Advanced Industrial Science and Technology (AIST),
Umezono 1-1-1, Tsukuba, Ibaraki 305-8568, Japan.
A paper by Kitamura, Tsuji and Aoki that designed a topological Mott insulator (where a fermion system spontaneously becomes a topological insulator due to interactions) for cold-atom systems in optical lattices with a confirmation by a first-principles method for cold-atom systems extended to non-collinear spin structures [Sota Kitamura, Naoto Tsuji and Hideo Aoki: An interaction-driven topological insulator in fermionic cold atoms on an optical lattice --- A design with a density functional formalism (arXiv:1411.3345)] is now published in Phys. Rev. Lett. 115, 045304 (2015).
Dr Shintaro Takayoshi joined the group as a reseach associate.
Dr Naoto Tsuji, the research associate in the group, has moved to the Center for Emergent Matter Science, RIKEN, from April 2015.
A review on the iron-based superconductors by Aoki and Prof. Hosono (Tokyo Institute of Technology) is published in "Physics World" [Hideo Aoki and Hideo Hosono: A superconducting surprise comes of age, Physics Worl}, Feb. 2015, p.31].

2014

A long-sought-after non-cuprate high-Tc superconductor was recently been discovered in Stanford in a nickelate, (Nd,Sr)NiO2. Aoki, with Sakakibara et al have examined its superconductivity mechanism, starting from the first-principles electronic strucutre, and revealed that Tc in this material is suppressed due to a strong electron repulsion as compared with the cuprate [H. Sakakibara, H. Usui, K. Suzuki, T. Kotani, H. Aoki, and K. Kuroki: Model construction and a possibility of cuprate-like pairing in a new d9 nickelate superconductor (Nd,Sr)NiO2, Phys. Rev. Lett. 125, 077003 (2020) (Editors' suggestion)].
A group of Li (Chinese Academy of Sciences), Uchida et al discovered a new superconducting cuprate in Ba2CuO3+δ with Tc≃70 K in 2019. This material has vastly oxygen-vacant CuO planes, dramatically challenging the decades-old wisdom for the cuprates and hence call for a new paradigm. By introducing the Lieb lattice as a candidate structure, we show that the disrupted CuO network can indeed accommodate new pairing mechanisms, where the inter-orbital physics unexpectedly plays a key role and actually enhances superconductivity [K. Yamazaki, M. Ochi, D. Ogura, K. Kuroki, H. Eisaki, S. Uchida, and H. Aoki: Superconducting mechanism for a new-type cuprate Ba2CuO3+δ based on a multiorbital Lieb lattice model, Phys. Rev. Research 2, 033356 (2020)].
A group of Hafezi (Maryland) et al and Aoki have proposed an optical, in-situ method for controlling topological properties of graphene and related materials. There, spatially-periodic circularly-polarised light is irradiated, with which Chern numbers and Floquet band structures can be tuned [H. Kim, H. Dehghani, H. Aoki, I. Martin, and M. Hafezi: Optical imprinting of superlattices in 2D materials, Phys. Rev. Research 2, 043004 (2020)].
"Floquet topological insulator" (an emergence of a quantum Hall effect in zero external magnetic field in a honeycomb lattice illuminated by a circularly-polarised light), which has been predicted by Takashi Oka and Hideo Aoki [Phys. Rev. B 79, 081406(R) (2009)], is now demonstrated experimentally in a cold-atom system on a honeycomb optical lattice by Esslinger's group in ETH Zurich [G. Jotzu et al, Nature 515, 237 (2014)].
Our paper that theoretically indicated the existence of a supersolid phase in an electron-phonon system [Yuta Murakami, Philipp Werner, Naoto Tsuji and Hideo Aoki: Supersolid phase accompanied by a quantum critical point in the intermediate coupling regime of the Holstein model (arXiv:1402.6456)] has been accepted for publication in Phys. Rev. Lett.
Our theoretical paper on the iron pnictides [K. Kuroki, S. Onari, R. Arita, H. Usui, Y. Tanaka, H. Kontani and H. Aoki: Unconventional superconductivity originating from disconnected Fermi surfaces in LaO1-xFxFeAs, Phys. Rev. Lett. 101, 087004 (2008)] has now been cited more than 900 times.
A strong THz laser light is shown to induce oscillations of the superconducting order parameter in NbN with twice the frequency of the THz field in an experiment done by Professor Shimano's group in our department. The result is theoretically captured as a collective precession of Anderson's pseudospins in ac driving fields. Specifically, a resonance between the field and the Higgs amplitude mode of the superconductor is shown, both experimentally and theoretically, to induce large THz third-harmonic generation. The experiment-theory joint paper is now published on 5 September in Science 345, 1145 (2014).
A strong THz laser light is shown to induce oscillations of the superconducting order parameter in NbN with twice the frequency of the THz field in an experiment done by Professor Shimano's group in our department. The result is theoretically captured as a collective precession of Anderson’s pseudospins in ac driving fields. Specifically, a resonance between the field and the Higgs amplitude mode of the superconductor is shown, both experimentally and theoretically, to induce large THz third-harmonic generation. The experiment-theory joint paper is now published in Science Express, 10 July 2014 issue.
A review article, Hideo Aoki, Naoto Tsuji, Martin Eckstein, Marcus Kollar, Takashi Oka and Philipp Werner: Nonequilibrium dynamical mean-field theory and its applications (arXiv:1310.5329), is now published in Reviews of Modern Physics 86, 779 (2014).
A review article, Hideo Aoki, Naoto Tsuji, Martin Eckstein, Marcus Kollar, Takashi Oka and Philipp Werner: Nonequilibrium dynamical mean-field theory and its applications (arXiv:1310.5329), has been accepted for publication in Reviews of Modern Physics.

2013

A book on graphene,
Hideo Aoki and Mildred S. Dresselhaus (ed.): Physics of Graphene (Springer, 2013),
has been published online (while the printed version will appear in Jan. 2014).
Aoki, Tsuji, Eckstein, Kollar, Oka and Werner have written a review article on the nonequilibrium DMFT and its applications to correlated electron systems,
Hideo Aoki, Naoto Tsuji, Martin Eckstein, Marcus Kollar, Takashi Oka and Philipp Werner: Nonequilibrium dynamical mean-field theory and its applications,
which has been posted as arXiv:1310.5329.
A topological phenomenon predicted by Oka and Aoki in 2009 [an emergence of a topological gap and associated Hall effect in zero magnetic field occurring in honeycom systems such as graphene illuminated by a circularly-polarised light; Takashi Oka and Hideo Aoki: Photovoltaic Hall effect in graphene, Phys. Rev. B 79, 081406(R) (2009)]
has been experimentally detected for Dirac fermions on a topological insulator [Y. H. Wang, H. Steinberg, P. Jarillo-Herrero and N. Gedik: Observation of Floquet-Bloch States on the Surface of a Topological Insulator, Science 342, 453 (2013)].i
A theoretical prediction that a graphene quantum dot can realise an analogue and magnetic-field control of the "charged vacuum", which has been considered for supercritical nuclei with atomic number much exceeding 137 accompanied by spontaneous electron-positoron pair production, is published [P. A. Maksym and H. Aoki: Magnetic field controlled vacuum charge in graphene quantum dots with a mass gap, Phys. Rev. B 88, 081406(R) (2013)] as a rapid communication.
Our theoretical paper on the iron pnictides
[K. Kuroki, S. Onari, R. Arita, H. Usui, Y. Tanaka, H. Kontani and H. Aoki:
Unconventional superconductivity originating from disconnected Fermi surfaces in LaO1-xFxFeAs, Phys. Rev. Lett. 101, 087004 (2008)]
has now been cited more than 700 times.
Also, a later paper, K. Kuroki et al: Pnictogen height as a possible switch between high-Tc nodeless and low-Tc nodal pairings in the iron-based superconductors, Phys. Rev. B 79, 224511 (2009), has now been cited more than 300 times.
The optical graphene quantum Hall effect (i.e., the plateau structure in the optical Hall conductivity in graphene), which has been theoretically predicted by Morimoto, Hatsugai and Aoki [Phys. Rev. Lett. 103, 116803 (2009)], is now experimentally detected from Faraday and Kerr rotations by the group led by Prof. R. Shimano, and the paper has now been published in Nature Communications (DOI: 10.1038/ncomms2866) [R. Shimano, G. Yumoto, J. Y. Yoo, R. Matsunaga, S. Tanabe, H. Hibino, T. Morimoto and H. Aoki: Quantum Faraday and Kerr rotations in graphene, Nature Commun., to be published; a collaboration with NTT and Riken].

2012

A paper on the aromatic (picene) superconductor,
Takashi Kambe, Xuexia He, Yosuke Takahashi, Yusuke Yamanari, Kazuya Teranishi, Hiroki Mitamura,, Seizi Shibasaki, Keitaro Tomita, Ritsuko Eguchi, Hidenori Goto, Yasuhiro Takabayashi, Takashi Kato, Akihiko Fujiwara, Toshikaze Kariyado, Hideo Aoki and Yoshihiro Kubozono:
Synthesis and physical properties of metal-doped picene solids,
Phys. Rev. B 86, 214507 (2012)
in which a selective synthesis of the Tc=18 K phase, and an enhancement of Tc under pressure are experimentally reported, with theoretical contributions from Kariyado and Aoki, has been selected as an Editors' Suggestion.
A theoretical proposal for a peculiar manifestation of orbital magnetism in the absence of spin-orbit interactions in a zeolite-templated carbon system has been publised as
Takashi Koretsune, Ryotaro Arita, and Hideo Aoki, Phys. Rev. B 86, 125207 (2012).
This has been highlighted in the PRB Kaleidoscope as
"A three-winged "pinwheel", a unit in a zeolite-templated carbon structure that is shown to accommodate a magneto-orbital effect without spin-orbit interactions."
Our theoretical paper on the iron pnictides
[K. Kuroki, S. Onari, R. Arita,
H. Usui, Y. Tanaka, H. Kontani and H. Aoki:
Unconventional superconductivity originating from
disconnected Fermi surfaces in LaO1-xFxFeAs,
Phys. Rev. Lett. 101, 087004 (2008)]
has now been cited more than 600 times.
Also, a later paper,
K. Kuroki et al: Pnictogen height as a possible switch between high-T-c
nodeless and low-T-c nodal pairings in the iron-based superconductors,
Phys. Rev. B 79, 224511 (2009), has been cited more than 230 times.
Solid picene, in which Kubozono's group has discovered superconductivity when doped with K atoms, has been analysed with UPS and LEED to probe the electronic structure by Ueno's group in Chiba University, with a theoretical analysis by Aoki's group, and the paper has been published in Phys. Rev. Lett. 108, 226401 (2012).
Prominent fractional quantum Hall states up to nu= 5/11 have been observed in a two-dimensional electron system confined at oxide (ZnO) heterointerface. From an analysis of the temperature dependence of the magnetotransport in terms of the composite fermion picture, strong interactions between composite fermions are suggested.
D.Maryenko, J.Falson, Y.Kozuka, A.Tsukazaki, M.Onoda, H.Aoki and M.Kawasaki:
Temperature dependent magnetotransport around nu = 1/2 in ZnO heterostructures,
has been published in Phys. Rev. Lett. 108, 186803 (2012)
A full paper that reveals key factors causing the strong
material-dependence in the high Tc cuprates,
H. Sakakibara, H. Usui, K. Kuroki, R. Arita and H. Aoki:
Origin of the material dependence of T_c in the single-layered
cuprates (arXiv:1112.0964),
has been accepted for publication in Phys. Rev. B 85, 064501
(2012) as an Editor's Suggestion.

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2011

First-principles electronic structure calculation
for K-doped coronene, which is the second aromatic
superconductor after K-doped picene reported by
Kubozono's group, has been published as
Taichi Kosugi, Takashi Miyake, Shoji Ishibashi,
Ryotaro Arita and Hideo Aoki:
Electronic structure of solid coronene: differences and commonalities to
picene,
Phys. Rev. B 84, 020507(R),
which is also selected as an Editors' Suggestion.
The paper,
Naoto Tsuji, Takashi Oka, Philipp Werner and Hideo Aoki:
Changing the interaction of lattice fermions dynamically
from repulsive to attractive in ac fields,
in which we have shown theoretically that a sudden application of an
intense ac field to correlated lattice fermions
effectively switches the interaction from repulsive to attractive,
accompanied by a negative temperature (population inversion), which
in turn suggests a possibility of dynamically induced
superconductivity, has been published in Phys. Rev. Lett. 106,
236401 (2011). The paper has been selected as an Editor's suggestion,
and also introduced by
James K. Freericks:
Changing repulsion into attraction with the quantum Hippy Hippy Shake,
Physics 4, 45 (2011)
http://physics.aps.org/articles/v4/45
as a Viewpoint article.
A video and the slides of the
talk given by Aoki at IPMU Focus Week "Condensed Matter
Physics Meets High Energy Physics" held on 8-12 February, 2010,
has been posted at a web page
http://member.ipmu.jp/cmphep2010/
A theoretical idea for realising the Nagaoka-like
ferromagnetism in a ladder structure for cold atoms
in optical lattices has been published as
M. Okumura, S. Yamada, M. Machida and H. Aoki:
Phase-separated ferromagnetism in spin-imbalanced Fermi atoms
Loaded on an optical ladder--- a DMRG study,
Phys. Rev. A 83, 031606(R) (2011).
A review on the quantum Hall effect,
Hideo Aoki: Integer quantum Hall effect,
is now published as a chapter in
Hiroshi Kamimura (ed.):
Comprehensive Semiconductor Science & Technology (Elsevier, 2011).
Our work,
Y. Ota, M. Machida, T. Koyama and H. Aoki:
Leggett's collective modes in multiband superfluids and
superconductors --- Multiple dynamical classes, arXiv:1008.3212,
in which three-band superconductors are shown to have
multiple collective (Leggett) excitation modes
with different masses, with an instability when the three
kinds of gauge-symmetry breaking are "frustrated" ,
has been published in Phys. Rev. B 83, 060507(R) (2011).
colloqium
Lecturer: Philipp Werner (ETH Zurich)
Title: "Interaction quenches and ramps in the Hubbard model"
Date: 2011/ 1/ 24(Mon) 16:00 - 17:30
Place: Rm 233 at Bld 1

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2010

colloqium
Lecturer: Takuya Kitagawa (Harvard University)
Title: "Topological characterization of periodically driven systems "
Date:2010/ 12/ 17(Fri) 17:00 - 18:30
Place:Rm 933 at Bld 1
While a massless Dirac particle has
half-integer quantum-Hall topological numbers,
known as an anomaly, it is interesting to
ask whether the quantum Hall
effect in lattice models can be decomposed into a half-integer
contributions from each Dirac cone. A study on this
(Haruki Watanabe, Yasuhiro Hatsugai and Hideo Aoki:
Half-integer contributions to the quantum
Hall conductivity from single Dirac cones,
(arXiv:1008.0130))
has been published in Phys. Rev. B 82, 241403(R) (2010).
colloqium
Lecturer: Koich Kusakabe (Osaka University)
Title: "Pair-Hopping Mechanism for Layered Superconductors"
Date:2010/ 10/ 12(Tue) 14:00 -
Place:Rm 933 at Bld 1
colloqium
Lecturer: Martin Eckstein (ETH)
Title:"Dynamical mean-field theory for the real-time evolution of correlated electron systems"
Date:2010/ 9/ 6(Mon) 15:00 - 16:30
Place:Rm 933 at Bld 1
colloqium
Lecturer: Werner Dietsche（Max-Planck-Institut fur Festkorperforschung）
Title:"The Exciton Condensate in Quantum-Hall Bilayers"
Date:2010/ 8/ 10(Tue) 16:00 - 17:30
Place:Rm 933 at Bld 1
A two-orbital study
[Hirofumi Sakakibara, Hidetomo Usui,
Kazuhiko Kuroki, Ryotaro Arita and Hideo Aoki:
Two orbital model explains
why the single-layer Hg cuprate have higher
superconducting transition temperature than the La cuprate]
(arXiv:1003.1770)
on the long-standing puzzle on why the single-layered cuprate
HgBa2CuO4+x(Tc~90K) has such a higher Tc than La2-x(Sr/Ba)xCuO4(Tsub>c~40K)
has been published in Phys. Rev. Lett. 105, 057003 (2010) .
An experiment in Professor Shimano's laboratory
[Y. Ikebe, T. Morimoto, R. Masutomi, T. Okamoto, H. Aoki and R. Shimano:
Optical Hall Effect in the Integer Quantum Hall Regime]
(arXiv:1004.0308)
jointly written with our theoretical group has
detected the "Optical Hall effect" (namely, the optical Hall conductivity
in the THz regime in the quantum Hall systems), which
has been theoretically predicted by
Takahiro Morimoto, Yasuhiro Hatsugai and Hideo Aoki:
Optical Hall conductivity in ordinary and graphene QHE systems,
Phys. Rev. Lett. 103, 116803 (2009).
The experimental paper is now published in
Physical Review Letters 104, 256802 (2010).
Following the publication of the experimental work by Kubozono's group
on the discovery of the first aromatic superconductor as
R. Mitsuhashi et al, Nature 464, 76 (2010) on 4 March 2010,
the theoretical work on this material by Aoki's group
has been press released at
http://www.s.u-tokyo.ac.jp/press/press-2010-08en.html
IPMU Focus Week "Condensed Matter Physics Meets High
Energy Physics" has been held in February 2010, co-chaired
by Aoki and Professor Hiroshi Ooguri
（Caltech/IPMU). For details, visit
http://www.theory.caltech.edu/~ooguri/CMP-HEP/CMP-HEP.htm

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2009

A paper on the electronic structure of the
doped solid picene, the first aromatic organic
superconductor discovered by a group led by
Professor Kubozono of Okayama University,
has been published:
Taichi Kosugi, Takashi Miyake, Shoji Ishibashi, Ryotaro Arita
and Hideo Aoki:
First-Principles Electronic Structure of Solid Picene,
J. Phys. Soc. Jpn 78, 113704 (2009)
(arXiv:0910.3022).
colloqium
Lecturer:P. Werner (ETH)
Title:"Monte Carlo approach to transport and non-equilibrium problems"
Date:2009/ 10/ 20(Tue) 13:00 - 14:30
Place:Rm 447 at Bld 1
colloqium
Lecturer:Shin-ichiro Ideta (Science Faculty, Tokyo University)
Title:"ARPES study of the tri-layer Cuprate superconductor Bi2Sr2Ca2Cu3O10+d"
Date:2009/ 10/ 19(Mon) 15:30 - 17:00
Place:Rm 933 at Bld 1
Our work that has analysed the anomalous behaviour of the
Landau level at the Dirac point in the graphene quantum
Hall effect,
Tohru Kawarabayashi, Yasuhiro Hatsugai, Hideo Aoki:
"Quantum Hall plateau transition in graphene with correlated random
hopping" (arXiv:0904.1927)
has been published in Phys. Rev. Lett. 103, 116803 (2009).
The Letter has also been
highlighted in a Synopsis on the Physics website
with the link to the Synopsis:
http://physics.aps.org/synopsis-for/10.1103/PhysRevLett.103.156804
The paper on the ac (optical) response of the quantum
Hall systems,
Takahiro Morimoto, Yasuhiro Hatsugai and Hideo Aoki:
Optical Hall conductivity in ordinary and graphene QHE systems
(arXiv:0904.2438)
has been published in Phys. Rev. Lett. 103, 116803 (2009).
Press Releases
University of Tokyo Museum exhibition
"Iron, the core of existence through the
history of 13.7 billion years",
to which Professor Aoki has contributed,
is now open.
The paper on nonequilibrium states that are created
when an intense laser is irradiated to strongly correlated
electron systems
(Naoto Tsuji, Takashi Oka, and Hideo Aoki:
Nonequilibrium steady state in photoexcited correlated electrons with
dissipation, arXiv:0903.2332)
has been accepted for publication in Phys. Rev. Lett. 103, 047403 (2009)
GCOE (Global Center of Excellence) seminar
Lecturer:Prof. P. A. Maksym ( University of Leicester, Leicester, UK)
itle:"Electron confinement in graphene quantum dots"
Date:2009/ 7/ 13(Mon) 16:00 -
Place:Rm 933 at Bld 1
A theoretical paper [a full paper to PRL 101, 087004 (2008)] on the new iron-based superconductor,
Kazuhiko Kuroki, Hidetomo Usui, Seiichiro Onari, Ryotaro Arita and Hideo Aoki:Pnictogen height as a possible switch between high-$T_c$ nodeless and low-$T_c$ nodal pairings in the iron based superconductors,
Phys. Rev. B 79, 224511 (2009)has been selected by the editors of PRB to be an "Editors' Suggestion". (June 2009)
(external link to APS )

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