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ResercherID: Y. Hatsugai
[F]  2013 EMN West Meeting on Topological Insulators,  Houston, USA  Jan 7-10(2013) [ Web ]

Invited: "Symmetry protection in topological phases"
             Yasuhiro Hatsugai
One of the characteristic features of topological phases such as topological insulators is absence of the fundamental symmetry breaking which has been a basic concept in the description of conventional order. Still symmetry plays a central role for the topological phases as symmetry protection in several ways. Gapless node structure of anisotropic superconductors is topologically protected, which is a historical example [1,2]. Generically the symmetry governs the gapless phases with massless Dirac fermions in 2D, 3D and more [3,4] where the co-dimenison of the generic degeneracy is crucial. For the gapped phases, the symmetry again controls properties of the topological systems. In addition to the intrinsically quantized quantities such as the Chern numbers, one further has adiabatic invariants by symmetry protected quantization as the Z2 Berry phases and its generalization [4,5,6]. They are used as the topological order parameters. Specifically for the topological insulators, the time reversal symmetry (TR) and the associated Kramers (KR) degeneracy are fundamentally important. Then the natural tool for the description is a quaternion and the quaternionic Berry connections of the KR pair. Topological quantities with/without TR symmetry are described in a parallel way for the Chern numbers and symmetry protected quantized quantities [5]. Also the charge-flux duality of some 3D topological insulator on a frustrated lattice will be discussed [7].
1. E. I. Blount, Phys. Rev. B 32, 2935 (1985).
2. G. E. Volovik, JETP Lett. 66, 522 (1997).
3. M. Creutz, JHEP 04, 017 (2008).
4. Y. Hatsugai, J. Phys. Soc. Japan 75, 123601 (2006).
5. Y. Hatsugai, New J. Phys. 12, 065004 (2010).
6. Y. Hatsugai and I. Maruyama, EPL 95, 20003 (2011).
7. Y. Hatsugai and Y. Avishai, to be published.
[P] Seminar at M. Ueda Group, Univ. Tokyo, JAPAN, Jan 24 (2013)
[P] Topological states of matter, Aspen, USA Jan 13--18 (2013)

今年もやります。まずは量子力学3. 冬は 統計力学2. 平成29年の新年あけましておめでとうございます。今年もあと43日!
投稿者 : hatsugai 投稿日時: 2017-10-06 16:36:02 (77 ヒット)

The entanglement Chern numbers is a Chern number of an entanglement Hamiltonian which characterizes topological properties of a topological phase. Starting from a pure state density matrix of the ground state, one may obtain finite temperature (mixed state) density matrix by tracing out parts of the system. If the entanglement hamiltonian has a finite energy gap, the Chern number is well defined by lowering the temperature. We apply the concept for the 3D topological phases.The parity of the number of the Weyl point gives a well defined topological number to distinguish the the state is topologically non trivial. Have a look at arXiv 1708.03722 . The paper has been accepted for publication in Physical Review B.

投稿者 : hatsugai 投稿日時: 2017-08-17 17:01:30 (300 ヒット)

初貝研究室では今回助教2名を公募いたします(公募締め切り2017年9月15日)。委細は [助教公募] をご確認ください。適任者のご推薦、ご応募の方よろしくお願いいたします。

投稿者 : hatsugai 投稿日時: 2017-08-17 17:00:09 (342 ヒット)

We are organizing a Japan-Swiss workshop TTCM2017 at EPOCHAL Tsukuba, Sep.10-13 (2017). Limited number of posters will be still accepted.

投稿者 : hatsugai 投稿日時: 2017-08-03 13:38:17 (263 ヒット)

A numerical scheme to calculate the many body Chern number for a ground state multiplet is formulated and explicitly given for projected bands of any lattice. We demonstrate its validity for lattice analogue of the nu=1/3 and 1/2 states. The string gauge to realize the minimum flux compatible with the periodicity of the unit cell is also presented. [arXiv:1707.06722]. The paper is published in JPSJ lett.

    [0] バルクとエッジ
    [1] 集中講義
    [2] 原論文と解説
    [3] トポロジカル秩序とベリー接続:日本物理学会誌 「解説」 [JPS-HP] [pdf]
    [4] "Band gap, dangling bond and spin : a physicist's viewpoint" [pdf] [Web]
    科研費 1992年度:電子系スピン系におけるトポロジカル効果
    科研費 1994年度:物性論におけるトポロジーと幾何学的位相
    [1] MIT, Boston (2003)
    [2] APS/JPS March Meeting (2004)
    [3] JPS Fall meeting, JAPAN (2004)
    [4] APS/JPS March meeting (2005)
    [5] JPS Fall meeting (2005):Entanglement
    [6] Superclean workshop, Nasu (2006)
    [7] MPIPKS, Dresden (2006)
    [8] KEK, Tsukuba (2007)
    [9] ETH, Zurich (2008)
    [10] ICREA, Sant Benet (2009)
    [11] JPS Meeting, Kumamoto (2009)
    [12]HMF19, Fukuoka (2010)
    [13] NTU, Singapore (2011)
    [14] ICTP, Trieste (2011)
    [15] Villa conf., Orland (2012)
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