Evidence for a spontaneous gapped state in ultraclean bilayer graphene

Proc Natl Acad Sci U S A. 2012 Jul 3;109(27):10802-5. doi: 10.1073/pnas.1205978109. Epub 2012 Jun 8.

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.

Publication types

  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, Non-P.H.S.

MeSH terms

  • Electric Conductivity
  • Electrochemistry / methods
  • Electronics / methods*
  • Electrons
  • Graphite / chemistry*
  • Iron / chemistry
  • Magnetics / methods*
  • Quantum Theory*

Substances

  • Graphite
  • Iron