Evidence for a spontaneous gapped state in ultraclean bilayer graphene

Abstract

At the charge neutrality point, bilayer graphene (BLG) is strongly susceptible to electronic interactions and is expected to undergo a phase transition to a state with spontaneously broken symmetries. By systematically investigating a large number of single-and double-gated BLG devices, we observe a bimodal distribution of minimum conductivities at the charge neutrality point. Although σ min is often approximately 2–3 e 2 / h (where e is the electron charge and h is Planck’s constant), it is several orders of magnitude smaller in BLG devices that have both high mobility and low extrinsic doping. The insulating state in the latter samples appears below a transition temperature T c of approximately 5 K and has a T = 0 energy gap of approximately 3 meV. Transitions between these different states can be tuned by adjusting disorder or carrier density.

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Affiliated Institutions

• Florida State University US
• University of Maryland, College Park US
• University of Pennsylvania US
• National High Magnetic Field Laboratory US
• California Institute of Technology US
• University of California, Riverside US
• The University of Texas at Austin US

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