Purely Rotational Symmetry-Protected Topological Crystalline Insulator α-Bi<sub>4</sub>Br<sub>4</sub>

ORAL

Abstract

Recent theoretical advances have proposed a new class of topological crystalline insulator (TCI) phases protected by rotational symmetries. Distinct from topological insulators (TIs), rotational symmetry-protected TCIs are expected to show unique topologically protected boundary modes: First, the surface normal to the rotational axis features ``unpinned'' Dirac surface states whose Dirac points are located at generic k points. Second, due to the ``higher-order'' bulk boundary correspondence, a 3D TCI also supports 1D helical edge states. Despite the unique topological electronic properties, to date, purely rotational symmetry-protected TCIs remain elusive in real materials. Using first-principles band calculations and theoretical modeling, we identify the van der Waals material α-Bi4Br4 as a TCI purely protected by rotation symmetry. We show that the α-Bi4Br4's (010) surface exhibits a pair of unpinned topological Dirac fermions protected by the two-fold rotational axis. These unpinned Dirac fermions show an exotic spin texture highly favorable for spin transport and a band structure consisting of van Hove singularities due to Lifshitz transition.

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Presenters

  • Chuang-Han Hsu

    • Department of Physics, National University of Singapore

Authors

  • Chuang-Han Hsu

    • Department of Physics, National University of Singapore

  • Tay-Rong Chang

    • National Cheng Kung University
    • Physics, National Cheng Chung University
    • Physics, National Cheng Kung University, Tainan, 701, Taiwan
    • Department of Physics, National Cheng Kung University
    • Physics, National Tsing Hua University
    • Physics, National Cheng Kung University

  • XIAOTING ZHOU

    • Physics, National Cheng Kung University, Tainan, 701, Taiwan
    • National Cheng Kung University
    • Department of Physics, National Cheng Kung University

  • Qiong Ma

    • Massachusetts Institute of Technology
    • Department of Physics, Massachusetts Institute of Technology

  • Nuh Gedik

    • Physics, Massachusetts Institute of Technology
    • Massachusetts Inst of Tech-MIT
    • Massachusetts Institute of Technology
    • Department of Physics, Massachusetts Institute of Technology

  • Arun Bansil

    • Northeastern University
    • Department of Physics, Northeastern University

  • Vitor Pereira

    • Centre for Advanced 2D Materials, National University of Singapore, 6 Science Drive 2, Singapore 117546
    • National University of Singapore
    • Department of Physics, National University of Singapore
    • Centre for Advanced 2D Materials, National University of Singapore

  • Liang Fu

    • Massachusetts Institute of Technology
    • MIT
    • Department of Physics, Massachusetts Institute of Technology

  • Suyang Xu

    • Department of Physics, Massachusetts Institute of Technology
    • Massachusetts Institute of Technology
    • MIT
    • Physics, MIT
    • Department of Physics, Massachusetts Institute of Technology, Cambridge

  • Hsin Lin

    • Academia Sinica
    • Institute of Physics, Academia Sinica
    • Physics, Academia Sinica, Taipei 11529, Taiwan
    • Institute of Physics, Academia Sinica, Taipei 11529, Taiwan
    • Physics, Academia Sinica
    • Department of Physics, National University of Singapore
    • National University of Singapore
    • Academia Sinica, Taipei, Taiwan