Dominant 1/3-filling Correlated Insulator States and Orbital Geometric Frustration in Twisted Bilayer Graphene

ORAL

Abstract

Geometric frustration is a phenomenon in a lattice system where not all interactions can be satisfied, the simplest example being antiferromagnetically coupled spins on a triangular lattice. Frustrated systems are characterized by their many nearly degenerate ground states, leading to non-trivial phases such as spin ice and spin liquids. To date most studies are on geometric frustration of spins; much less explored is orbital geometric frustration. For electrons in twisted bilayer graphene at denominator 3 fractional filling, Coulomb interactions and the Wannier orbital shapes are predicted to strongly constrain spatial charge ordering, leading to geometrically frustrated ground states that produce a new class of correlated insulators. Here we report the observation of dominant denominator 3 fractional filling insulating states in large angle twisted bilayer graphene; these states persist in magnetic fields and display magnetic ordering signatures and tripled unit cell reconstruction. These results are in agreement with a strong-coupling theory of symmetry-breaking of geometrically frustrated fractional states.

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Presenters

  • Haidong Tian

    • The Ohio State University
    • Ohio State University

Authors

  • Haidong Tian

    • The Ohio State University
    • Ohio State University

  • Emilio A Codecido

    • Ohio State Univ - Columbus

  • Dan Mao

    • Cornell University

  • Kevin Zhang

    • Cornell University

  • Shi Che

    • Ohio State Univ - Columbus

  • Kenji Watanabe

    • National Institute for Materials Science
    • NIMS
    • Research Center for Electronic and Optical Materials, National Institute for Materials Science
    • Research Center for Functional Materials, National Institute for Materials Science, 1-1 Namiki, Tsukuba 305-0044, Japan
    • National Institute for Material Science

  • Takashi Taniguchi

    • Kyoto Univ
    • National Institute for Materials Science
    • Research Center for Materials Nanoarchitectonics
    • Research Center for Materials Nanoarchitectonics, National Institute for Materials Science
    • National Institute for Materials Sciences
    • NIMS
    • International Center for Materials Nanoarchitectonics, National Institute for Materials Science, 1-1 Namiki, Tsukuba 305-0044, Japan
    • National Institute for Material Science
    • International Center for Materials Nanoarchitectonics, NIMS, Japan
    • International Center for Materials Nanoarchitectonics, Tsukuba
    • National Institue for Materials Science
    • Kyoto University
    • National Institute of Materials Science
    • International Center for Materials Nanoarchitectonics and National Institute for Materials Science

  • Dmitry Smirnov

    • National High Magnetic Field Laboratory

  • Eun-Ah Kim

    • Cornell University

  • Marc Bockrath

    • Ohio State University

  • Chun Ning Lau

    • Ohio State University
    • Ohio State Univ - Columbus