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HATSUGAI   Lab.     Institute of Physics, University of Tsukuba

L: Topological stability of Dirac cones, merging & C: fractal in graphene (Flying Butterfly) & R: Non Abelian gauge structure in solids
Refereneces :
[1] Y. Hatsugai, T. Fukui, H. Aoki, Phys. Rev. B 74, 205414 (2006) : [Journal Link] , arXiv:cond-mat/0607669
"Topological analysis of the quantum Hall effect in graphene"
[2] Y. Hatsugai, J. Phys. Soc. Jpn. 73, 2604 (2004) : [Journal Link] , arXiv:cond-mat/0405551
"Explicit Gauge Fixing for Degenerate Multiplets: A Generic Setup for Topological Orders"

Hatsugai Group, Condensed Matter Theory

Targets of our research is to explore new insight and find novel physical principles in condensed matter materials and phenomena. We have been working on the following topics. [paper]

[1] Geometrical phases of condensed matter physics
Target material and phenomena
(1) Graphene as a relativistic Dirac particle in solid states
(2) Quantum Hall effects as typical topological insulators
(3) Quantum spin Hall phase as a time reversal invariant topological insulator
(4) Electrons with strong correlation as non trivial quantum liquids
(5) Exotic superconductivity with anisotropic pairing
(6) Frustrated magnets as typical spin liquids
(7) Semiconductor nano-structures as a playground of novel quantum phenomena
(8) Universal edge states in quantum (spin) Hall effects, Haldane magnets, photonic crystals and cold atoms
(9) Aharonov-Bohm effect and its generalization

Theoretical methods and concepts
(1) Non-Abelian gauge structures of the Berry connections
(2) Berry connections and their generalization
(3) Quantum order parameters by the Chern numbers and generic Berry phases
(4) Theory of generic Aharnov-Bohm effects
(5) Entanglement entropy of quantum liquids and spin liquids
(6) Universality of the Bulk-Edge correspondence
(7) Characterization of topological orders in quantum liquids

[2] Novel quantum phenomena in real material and their relation to the emerging mathematical concepts as quantum group
Some works [Link1][Link2]
[3] Novel techniques to study ferimonic many body systems with strong correlation
Basic work [Link]
[4] Realistic electronic structures & topological quantities
One of my basic works [Link]


Let me explain what we are interested in!
Class & Theses
Information about the courses & theses. Japanese only at a moment
Who we are!
Coming seminar
How to join us
Information to join us:

  • Graduate courses at Univ. of Tsukuba [Web]
  • Contact me before taking the exam !

Information for access. How to reach us.

Institute of Physics
University of Tsukuba
1-1-1 Tennodai
Ibaraki 305-8571

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Year 2013
A HAPPY NEW YEAR 2019, 79 days left this year !
Recent News
Poster : hatsugai on 2019-09-30 11:19:28 (106 reads)

Exact flatness of energy bands implies some reasons behind. Here we present one of them, "molecular orbital (MO) representation", which seems to be applied for various classes of tight binding models. Mathematically if the rank of the hamiltonian as a linear operator is less than the number of atomic sites, the kernel of the linear operator has a finite dimension. This is the zero mode flat band. The MO rep. presents nice physical reasons for it. Original proposal by YH with Isao Maruyama in 2011 in EPL and arXiv is counting dimensions of non-orthogonal projections but the hopping of the MO's is allowed as we pointed out (it should be). It's a fun to guess what kinds of the MO representation is possible for a known flat band system. Try ! Also several physical reason why the flat band crosses/touches to dispersive bands in many cases are discussed. Our new paper has appeared in EPL, "Molecular-orbital representation of generic flat-band models", by T. Mizoguchi and Y. Hatsugai , also arXiv.

Poster : hatsugai on 2019-09-10 11:03:57 (101 reads)

I wrote a small article "So Small Implies So Large: For a Material Design" in the "News and comment" section of the JPSJ in relation to a recent interesting paper by Toshikaze Kariyado. Material deformation induces a gauge field that modifies electronic structure and may result in the Landau levels without breaking time reversal. Have a look at.

Poster : hatsugai on 2019-09-09 22:11:58 (107 reads)

Our paper "Higher-Order Topological Phase in a Honeycomb-Lattice Model with Anti-Kekulé Distortion" by Tomonari Mizoguchi, Hiromu Araki, and Yasuhiro Hatsugai, has appeared in J. Phys. Soc. Jpn. 88, 104703 (2019). One can access also via arXiv:1906.07928. Z6 quantization in honeycomb structure is the key. Have a look at.

Poster : hatsugai on 2019-08-26 14:24:32 (149 reads)

Ryo Okugawa (WPI-AIMR, Tohoku Univ.) will be telling us on his recent work as a title "Chiral-symmetry protected second-order topological phases" on Sep. 18 (2019). Rm. D301 from 13:30pm. Join us.

Poster : hatsugai on 2019-08-08 00:43:18 (151 reads)

Due to an intrinsic symmetry of a mechanical system with friction governed by the Newton equation, exceptional rings appear in two dimensions. We have demonstrated it and classification of symmetry-protected non-Hermitian degeneracies is addressed putting a focus on the symmetry. The paper is published in Physical Review B, "Exceptional rings protected by emergent symmetry for mechanical systems" by Tsuneya Yoshida and Yasuhiro Hatsugai. You may find also here arXiv:1904.10764.

    Bulk-edge correspondence
    [0] バルクとエッジ
    [1] Focus lecture
    [2] Original papers
    [3] Japanese Physical Society monthly issue Commentary (Only Japanese except abstract) [pdf]
    [4] "Band gap, dangling bond and spin : a physicist's viewpoint" [pdf]
    Topological phases
    [0]Historical project
    KAKEN-HI DB FY1992 : Topological effects in electronic/spin systems
    KAKEN-HI DB FY1994 : Topology & geometrical phases in condensed matter physics
    Some of my talk files
    [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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