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Levin, Andrei

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Levin

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Andrei

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Levin, Andrei

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2013 - 20142

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Author's Publications: search.filters.isAuthorOfPublication.1c9d6eb1-af95-4692-aae5-976632f8a600

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    Electron-hole asymmetric integer and fractional quantum Hall effect in bilayer graphene
    (American Association for the Advancement of Science (AAAS), 2014) Kou, Angela; Feldman, Benjamin Ezekiel; Levin, Andrei; Halperin, Bertrand; Watanabe, Kenji; Taniguchi, Takashi; Yacoby, Amir
    The nature of fractional quantum Hall (FQH) states is determined by the interplay between the Coulomb interaction and the symmetries of the system. The unique combination of spin, valley, and orbital degeneracies in bilayer graphene is predicted to produce novel and tunable FQH ground states. Here we present local electronic compressibility measurements of the FQH effect in the lowest Landau level of bilayer graphene. We observe incompressible FQH states at filling factors \(\nu = 2p + 2/3\) with hints of additional states appearing at \(\nu = 2p + 3/5\), where p = -2,-1, 0, and 1. This sequence of states breaks particle-hole symmetry and instead obeys a \(\nu \rightarrow \nu + 2\) symmetry, which highlights the importance of the orbital degeneracy for many-body states in bilayer graphene.
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    Fractional Quantum Hall Phase Transitions and Four-Flux States in Graphene
    (American Physical Society (APS), 2013) Feldman, Benjamin Ezekiel; Levin, Andrei; Krauss, Benjamin; Abanin, Dmitry; Halperin, Bertrand; Smet, Jurgen H.; Yacoby, Amir
    Graphene and its multilayers have attracted considerable interest because their fourfold spin and valley degeneracy enables a rich variety of broken-symmetry states arising from electron-electron interactions, and raises the prospect of controlled phase transitions among them. Here we report local electronic compressibility measurements of ultraclean suspended graphene that reveal a multitude of fractional quantum Hall states surrounding filling factors \(\nu =−1/2\) and \(−1/4\). Several of these states exhibit phase transitions that indicate abrupt changes in the underlying order, and we observe many additional oscillations in compressibility as \(\nu \) approaches \(−1/2\), suggesting further changes in spin and/or valley polarization. We use a simple model based on crossing Landau levels of composite fermions with different internal degrees of freedom to explain many qualitative features of the experimental data. Our results add to the diverse array of many-body states observed in graphene and demonstrate substantial control over their order parameters.