Extended Fractional Chern Insulators Near Half Flux in Twisted Bilayer Graphene Above the Magic Angle

ORAL  · Invited

Abstract

When a Chern band is partially filled, a fractional Chern insulator (FCI)---the lattice analog of a fractional quantum Hall state---can arise. Though the full range of possible scenarios for producing such a state is not established, the most tractable models combine strong electronic interactions with the quantum geometry of the parent Chern band meeting specific criteria. In twisted bilayer graphene, the importance of interactions can be tuned by varying the interlayer twist. Here, we study a sample with twist $\sim 1.4$\textdegree, large enough to suppress the zero-field correlated states. We find that applying a strong magnetic field restores the importance of electron-electron interactions: at nearly half a magnetic flux quantum per moir\'e unit cell, deep in the Hofstadter regime, odd-denominator FCIs appear in multiple Hofstadter subbands. These fractional states persist over larger ranges of density, and are more robustly quantized, than nearby integer states, opposite to what is seen in other fractional quantum Hall or FCI systems.

*This work was supported by the U.S. Department of Energy, Office of Science, Basic Energy Sciences, Materials Sciences and Engineering Division, under Contract DE-AC02-76SF00515. Device fabrication was performed at the Stanford Nano Shared Facilities, supported by the National Science Foundation (NSF) under award ECCS-2026822. Support for supplies came from the Ross M. Brown Family Foundation and the Gordon and Betty Moore Foundation's EPiQS Initiative (Grant GBMF9460). J.K. acknowledges support from the National Natural Science Foundation of China (Grant 12074276), the Double First-Class Initiative Fund, and the start-up grant of ShanghaiTech University. O.V. was funded in part by the Gordon and Betty Moore Foundation's EPiQS Initiative (GBMF11070) and by the National High Magnetic Field Laboratory (NSF DMR-2128556, State of Florida). K.W. and T.T. acknowledge JSPS KAKENHI support (Grants 19H05790, 20H00354, 21H05233). Part of this work was performed at the National High Magnetic Field Laboratory, supported by the NSF (DMR-1644779) and the State of Florida. 

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Publication: https://arxiv.org/abs/2503.12819

Presenters

  • Aaron Layne Sharpe

    • Stanford University
    • SLAC National Accelerator Laboratory

Authors

  • Aaron Layne Sharpe

    • Stanford University
    • SLAC National Accelerator Laboratory

  • Joe Finney

    • Stanford Univ

  • Linsey K Rodenbach

    • Zurich Instruments, Inc.
    • NVIDIA

  • Jian Kang

    • ShanghaiTech University
    • Soochow Univ

  • Xiaoyu Wang

    • National High Magnetic Field Laboratory

  • Kenji Watanabe

    • National Institute for Materials Science
    • Research Center for Functional Materials, National Institute of Materials Science, 1-1 Namiki Tsukuba, Ibaraki 305-0044, Japan

  • Takashi Taniguchi

    • National Institute for Materials Science
    • Research Center for Materials Nanoarchitectonics, National Institute for Materials Science
    • International Center for Materials Nanoarchitectonics, National Institute of Materials Science, 1-1 Namiki Tsukuba, Ibaraki 305-0044, Japan
    • Research Center for Functional Materials, National Institute of Materials Science, 1-1 Namiki Tsukuba, Ibaraki 305-0044, Japan

  • Marc Kastner

    • Stanford University
    • Stanford Institute for Materials & Energy Sciences, Stanford University

  • Oskar Vafek

    • University of Minnesota Twin Cities

  • David Goldhaber-Gordon

    • Stanford University
    • Stanford Institute for Materials & Energy Sciences, Stanford University