期刊
SCIENCE
卷 330, 期 6005, 页码 812-816出版社
AMER ASSOC ADVANCEMENT SCIENCE
DOI: 10.1126/science.1194988
关键词
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资金
- U. S. Department of Energy Office of Science (DOE SCGF)
- U.S. DOE, Office of Basic Energy Sciences, Division of Materials Sciences and Engineering [DE-SC0001819]
- 2009 U.S. Office of Naval Research Multi University Research Initiative (MURI) on Graphene Advanced Terahertz Engineering (Gate) at Massachusetts Institute of Technology, Harvard
- Boston University
- Harvard's Nanoscale Science and Engineering Center under NSF [PHY-0646094]
- U.S. Department of Energy (DOE) [DE-SC0001819] Funding Source: U.S. Department of Energy (DOE)
The single-particle energy spectra of graphene and its bilayer counterpart exhibit multiple degeneracies that arise through inherent symmetries. Interactions among charge carriers should spontaneously break these symmetries and lead to ordered states that exhibit energy gaps. In the quantum Hall regime, these states are predicted to be ferromagnetic in nature, whereby the system becomes spin polarized, layer polarized, or both. The parabolic dispersion of bilayer graphene makes it susceptible to interaction-induced symmetry breaking even at zero magnetic field. We investigated the underlying order of the various broken-symmetry states in bilayer graphene suspended between top and bottom gate electrodes. We deduced the order parameter of the various quantum Hall ferromagnetic states by controllably breaking the spin and sublattice symmetries. At small carrier density, we identified three distinct broken-symmetry states, one of which is consistent with either spontaneously broken time-reversal symmetry or spontaneously broken rotational symmetry.
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