Anomalous Hall effect at half filling in twisted bilayer graphene

ORAL

Abstract

Magic-angle twisted bilayer graphene (MA-tBLG) hosts a wealth of symmetry-broken states arising due to strong Coulomb interactions in the moiré flat bands. Orbital magnetic states, with spontaneously broken time-reversal symmetry at zero field, have been previously reported at odd integer filling factors (ν = +1 and +3) in a small number of devices, manifesting as an anomalous Hall effect (AHE). Here, we will discuss two tBLG devices with twist angles slightly away from the magic angle (0.96° and 1.2°). Surprisingly, both devices display an AHE at half filling (ν = +2 and -2, respectively), which has not been observed previously. These states are not anticipated in existing theoretical models owing to competing intervalley-coherent, spin-polarized, and/or valley Hall states with lower energy. We suggest that our observations at half filling likely correspond to valley polarized phases stabilized by the combination of the increased bandwidth away from the magic angle and symmetry-breaking substrate potentials from the boron nitride. We do not observe superconductivity in our devices, hinting at a possible antagonistic relationship between the two. Our results motivate further investigation of tBLG away from the strongly coupled limit.

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Presenters

  • Chun-Chih Tseng

    • University of Washington

Authors

  • Chun-Chih Tseng

    • University of Washington

  • Xuetao Ma

    • University of Washington

  • Zhaoyu Liu

    • University of Washington

  • 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

  • Jiun-Haw Chu

    • University of Washington
    • University of Washington, Seattle, Washington, USA

  • Matthew A Yankowitz

    • University of Washington