title: Local compressibility measurements of correlated states in suspended bilayer graphene.
abstract: Bilayer graphene has attracted considerable interest due to the important role played by many-body effects, particularly at low energies. Here we report local compressibility measurements of a suspended graphene bilayer. We find that the energy gaps at filling factors ν= ± 4 do not vanish at low fields, but instead merge into an incompressible region near the charge neutrality point at zero electric and magnetic field. These results indicate the existence of a zero-field ordered state and are consistent with the formation of either an anomalous quantum Hall state or a nematic phase with broken rotational symmetry. At higher fields, we measure the intrinsic energy gaps of broken-symmetry states at ν=0, ± 1, and ± 2, and find that they scale linearly with magnetic field, yet another manifestation of the strong Coulomb interactions in bilayer graphene.
authors.affiliation: Department of Physics, Harvard University, Cambridge, Massachusetts 02138, USA.
authors.forename: J
authors.initials: J
authors.lastname: Martin
authors.forename: B E
authors.initials: BE
authors.lastname: Feldman
authors.forename: R T
authors.initials: RT
authors.lastname: Weitz
authors.forename: M T
authors.initials: MT
authors.lastname: Allen
authors.forename: A
authors.initials: A
authors.lastname: Yacoby