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Topological crystalline insulator: from symmetry indicators to material discovery

ORAL

Abstract

Topological crystalline insulators (TCIs) are insulating electronic phases of matter in which the nontrivial topology is driven by crystalline symmetries. Recent theoretical advances have proposed new rotational-symmetry-protected TCI states that are expected to show unique topologically protected boundary modes. The surface normal to the rotational axis in these TCIs features ''unpinned'' Dirac surface states whose Dirac points are located at generic k points. Also, due to the ''higher-order'' bulk-boundary correspondence, such a 3D TCI supports 1D helical edge states. However, to date, rotational-symmetry-protected TCIs have remained elusive in real materials. We systematically examine the topological properties of the TCI states in Ca2As. On both the top and side surfaces, we show the presence of topological surface states protected independently by rotational and mirror symmetries [1]. We also discuss the van der Waals material α-Bi4Br4 and the pristine bulk bismuth and show that these materials harbor TCI states protected purely by rotation symmetry [2,3], even though these materials have been long thought to be topologically trivial.

[1] Phys. Rev. B, 98, 241104(R) (2018).
[2] 2D Materials 6, 031004 (2019).
[3] PNAS 116, 13255 (2019).

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Presenters

  • Tay-Rong Chang

    National Cheng Kung University, Physics, National Cheng Kung University, Department of Physics, National Cheng Kung University, National Cheng Kung University, Taiwan

Authors

  • Tay-Rong Chang

    National Cheng Kung University, Physics, National Cheng Kung University, Department of Physics, National Cheng Kung University, National Cheng Kung University, Taiwan

  • XIAOTING ZHOU

    National Cheng Kung University, Physics and Astronomy, California State University, Northridge, Department of Physics and Astronomy, California State University, Northridge

  • Chuang-Han Hsu

    National University of Singapore

  • Vitor Manuel Pereira

    Natl Univ of Singapore, National University of Singapore

  • Arun Bansil

    Northeastern University, Physics, Northeastern University

  • Suyang Xu

    Massachusetts Institute of Technology, Massachusetts Institute of Technology MIT, Physics, Massachusetts Institute of Technology, Harvard university, Harvard University, Havard University

  • Hsin Lin

    Academia Sinica, Physics, Academia Sinica, Institute of Physics, Academia Sinica, Taipei, Taiwan, Institute of Physics, Academia Sinica

  • Liang Fu

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