Quantum anomalous Hall state in bilayer graphene
Author(s)
Nandkishore, Rahul Mahajan; Levitov, Leonid
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We present a symmetry-based analysis of competition between different gapped states that have been proposed in bilayer graphene (BLG), which are all degenerate on a mean-field level. We classify the states in terms of a hidden SU(4) symmetry, and distinguish symmetry-protected degeneracies from accidental degeneracies. One of the states, which spontaneously breaks discrete time-reversal symmetry but no continuous symmetry, is identified as a quantum anomalous Hall (QAH) state, which exhibits quantum Hall effect at zero magnetic field. We investigate the lifting of the accidental degeneracies by thermal and zero-point fluctuations, taking account of the modes softened under renormalization group (RG). Working in a “saddle point plus quadratic fluctuations” approximation, we identify two types of RG-soft modes which have competing effects. Zero-point fluctuations, dominated by “transverse” modes which are unique to BLG, favor the QAH state. Thermal fluctuations, dominated by “longitudinal” modes, favor a SU(4) symmetry-breaking multiplet of states. We discuss the phenomenology and experimental signatures of the QAH state in BLG, and also propose a way to induce the QAH state using weak external magnetic fields.
Date issued
2010-09Department
Massachusetts Institute of Technology. Department of PhysicsJournal
Physical Review B
Publisher
American Physical Society
Citation
Nandkishore, Rahul, and Leonid Levitov. "Quantum anomalous Hall state in bilayer graphene." Physical Review B 82.11 (2010): 115124. © 2010 The American Physical Society
Version: Final published version
ISSN
1098-0121
1550-235X