Purely Rotational Symmetry-Protected Topological Crystalline Insulator α-Bi4Br4

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