STM spectroscopy of a gate-switchable moiré quantum anomalous Hall insulator

ORAL

Abstract

Twisting and stacking atomically-thin materials provides a versatile platform for investigating emergent quantum phases of matter driven by strong correlation and non-trivial topology. Novel phenomena such as correlated insulating states, unconventional superconductivity, and the quantum anomalous Hall (QAH) effect have been observed in different twisted moiré systems, but a full understanding of their underlying microscopic mechanisms remains a challenge. We have used scanning tunneling microscopy and spectroscopy to explore the interplay between correlation, topology, and local atomic structure in determining the behavior of a QAH insulator made from twisted monolayer-bilayer graphene (a sandwich of monolayer and bernal-stacked bilayer graphene with a small twist between them). We observe local spectroscopic signatures of correlated insulating states having total Chern number Ctot = +2 and -2 at ¾-filling of the conduction moiré mini-band and have characterized their evolution in an out-of-plane magnetic field. We have determined the relationship between topological behavior, local twist angle, and local hetero-strain, and show that Ctot can be switched between +2 and -2 via electrostatic gating only over a limited range of twist angle and strain. Electrical control of the Chern number results from a competition between the orbital magnetization of bulk bands and chiral edge states that is highly sensitive to distortion of the moiré superlattice.

*This work was supported by DOE and NSF.

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Publication: Canxun Zhang, Tiancong Zhu, Tomohiro Soejima, Salman Kahn, Kenji Watanabe, Takashi Taniguchi, Alex Zettl, Feng Wang, Michael P. Zaletel, Michael F. Crommie, "Local spectroscopy of gate-switchable Chern insulating states in twisted monolayer-bilayer graphene", arXiv:2210:06506.

Presenters

  • Salman A Kahn

    • University of California, Berkeley

Authors

  • Canxun Zhang

    • University of California, Berkeley

  • Tiancong Zhu

    • University of California, Berkeley
    • UC Berkeley

  • Tomohiro Soejima

    • University of California, Berkeley

  • Salman A Kahn

    • University of California, Berkeley

  • Kenji Watanabe

    • National Institute for Materials Science
    • Research Center for Functional Materials, National Institute of Materials Science
    • Research Center for Functional Materials, National Institute for Materials Science, 1-1 Namiki, Tsukuba 305-044, Japan
    • NIMS
    • Research Center for Functional Materials, National Institute for Materials Science
    • National Institute for Materials Science, Japan
    • Research Center for Functional Materials, National Institute for Materials Science, Tsukuba, Japan
    • NIMS Japan

  • Takashi Taniguchi

    • National Institute for Materials Science
    • Kyoto Univ
    • International Center for Materials Nanoarchitectonics, National Institute of Materials Science
    • Kyoto University
    • International Center for Materials Nanoarchitectonics, National Institute for Materials Science, 1-1 Namiki, Tsukuba 305-044, Japan
    • International Center for Materials Nanoarchitectonics, National Institute for Materials Science
    • National Institute for Materials Science, Japan
    • National Institute For Materials Science
    • NIMS
    • National Institute for Material Science
    • International Center for Materials Nanoarchitectonics, National Institute for Materials Science, Tsukuba, Japan
    • NIMS Japan

  • Alex K Zettl

    • University of California, Berkeley

  • feng wang

    • University of California, Berkeley

  • Michael P Zaletel

    • University of California, Berkeley
    • UC Berkeley

  • Michael F Crommie

    • University of California, Berkeley