Observation of room-temperature quantum spin Hall edge state in a higher order topological insulator Bi<sub>4</sub>Br<sub>4</sub>

ORAL

Abstract

Realizing macroscopic quantum phenomena at room temperature is a major pursuit in physics. The quantum spin Hall (QSH) state, a prototypical quantum phenomenon that features a two-dimensional insulating bulk and a topologically protected helical edge state at zero magnetic field, has not been realized at room temperature. Here, using scanning tunneling microscopy, we directly visualize a QSH edge state on the surface of the higher-order topological insulator Bi4Br4. We find that the atomically resolved lattice exhibits a large insulating gap of over 200meV while an atomically sharp monolayer step edge hosts an in-gap gapless state, which is the hallmark of topological bulk-boundary correspondence. An external magnetic field can gap the edge state, consistent with the time-reversal symmetry protection of the underlying topology. Furthermore, via directly identifying the geometrical hybridization of such edge states, we show the manifestation of the Z2 topology of the QSH state and visualize the building blocks of the higher-order topological insulator phase in Bi4Br4. Most notably, both the insulating gap and topological edge state persist up to 300K, pointing to the room temperature realization of the QSH state.

Reference: N. Shumia, Md. S. Hossain et al., arXiv:2110.05718 (2021).

*Experimental and theoretical work at Princeton: Gordon and Betty Moore Foundation (GBMF4547 and GBMF9461; M.Z.H.).Crystal growth is funded by the National Science Foundation of China (NSFC) (11734003), the National Key Research and Development Program of China (2016YFA0300600).European Union’s Horizon 2020 research and innovation program (ERC-StG-Neupert-757867-PARATOP); T.N.National Science Foundation Graduate Research Fellowship Program, grant no. DGE-1656466; T.A.C.NSFC (11574029) and the Strategic Priority Research Program of Chinese Academy of Sciences (XDB30000000); Y.G.Y.

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Publication: N. Shumiya, Md S. Hossain, J.-X. Yin, Z. Wang, M. Litskevich, C. Yoon, Y. Li, Y. Yang, Y.-X. Jiang, G. Cheng, Y.-C. Lin, Q. Zhang, Z.-J. Cheng, T. A. Cochran, D. Multer, X. P Yang, B. Casas, T.-R. Chang, T. Neupert, Z. Yuan, S. Jia, H. Lin, N. Yao, L. Balicas, F. Zhang, Y. Yao, and M. Z. Hasan, Room-temperature quantum spin Hall edge state in a higher-order topological insulator Bi4Br4, arXiv:2110.05718 (2021).

Presenters

  • Md. Shafayat Hossain

    • Princeton University

Authors

  • Md. Shafayat Hossain

    • Princeton University

  • Nana Shumiya

    • Princeton University

  • Jia-Xin Yin

    • Princeton University
    • Laboratory for Topological Quantum Matter and Advanced Spectroscopy (B7), Department of Physics, Princeton University, Princeton, New Jersey, USA.

  • Zhiwei Wang

    • Beijing Institute of Technology

  • Maksim Litskevich

    • Princeton University

  • Chiho Yoon

    • Seoul Natl Univ

  • Yongkai Li

    • Beijing Institute of Technology

  • Ying Yang

    • Beijing Institute of Technology

  • Yuxiao Jiang

    • Princeton University

  • Guangming Cheng

    • Princeton University

  • Yen-Chuan Lin

    • National Taiwan University

  • Qi Zhang

    • Princeton University

  • Zijia Cheng

    • Princeton University
    • Laboratory for Topological Quantum Matter and Advanced Spectroscopy (B7), Department of Physics, Princeton University, Princeton, New Jersey, USA.

  • Tyler A Cochran

    • Princeton University

  • Xian Yang

    • Princeton University

  • Brian Casas

    • FSU-NHMFL
    • National High Magnetic Field Laboratory

  • Tay-Rong Chang

    • Department of Physics, National Cheng Kung University, Tainan 70101, Taiwan
    • National Cheng Kung University

  • Titus Neupert

    • Univ of Zurich
    • University of Zurich
    • University of Zürich

  • Hsin Lin

    • Academia Sinica
    • Institute of Physics, Academia Sinica, Taiwan

  • Nan Yao

    • Princeton Institute for Science and Technology of Materials, Princeton University
    • Princeton University

  • Fan Zhang

    • UT Dallas
    • University of Texas at Dallas

  • Luis Balicas

    • National High Magnetic Field Laboratory

  • Yugui Yao

    • Beijing Institute of Technology

  • Zahid M Hasan

    • Princeton University
    • Laboratory for Topological Quantum Matter and Advanced Spectroscopy (B7), Department of Physics, Princeton University, Princeton, New Jersey, USA.