title: Competing ordered states with filling factor two in bilayer graphene.
abstract: The quantum Hall effect, in which a two-dimensional sample's Hall conductivities become quantized, is a remarkable transport anomaly commonly observed at strong magnetic fields. However, it may also appear at zero magnetic field if time-reversal symmetry is broken. Charge-neutral bilayer graphene is unstable to a variety of competing and closely related broken symmetry states, some of which have non-zero quantized Hall conductivities. Here we explore those states by stabilizing them with external fields. Transport spectroscopy measurements reveal two distinct states that have two quantum units of Hall conductivity, stabilized by large magnetic and electric fields, respectively. The majority spins of both phases form a quantum anomalous Hall state, and the minority spins constitute a Kekulé state with spontaneous valley coherence for phase I and a quantum valley Hall state for phase II. Our results shed light on the rich set of competing ordered states in bilayer graphene.
authors: 1] Department of Physics and Astronomy, University of California, Riverside, California 92521, USA [2] [3].
authors: J
authors: J
authors: Velasco
authors: 1] Department of Physics and Astronomy, University of California, Riverside, California 92521, USA [2].
authors: Y
authors: Y
authors: Lee
authors: 1] Department of Physics and Astronomy, University of Pennsylvania, Philadelphia, Pennsylvania 19104, USA [2] Department of Physics, University of Texas at Dallas, Richardson, Texas 75080, USA [3].
authors: F
authors: F
authors: Zhang
authors: Department of Physics and Astronomy, University of California, Riverside, California 92521, USA.
authors: K
authors: K
authors: Myhro
authors: Department of Physics and Astronomy, University of California, Riverside, California 92521, USA.
authors: D
authors: D
authors: Tran
authors: Department of Physics and Astronomy, University of California, Riverside, California 92521, USA.
authors: M
authors: M
authors: Deo
authors: National High Magnetic Field Laboratory, Tallahassee, Florida 32310, USA.
authors: D
authors: D
authors: Smirnov
authors: Department of Physics, University of Texas at Austin, Austin, Texas 78712, USA.
authors: A H
authors: AH
authors: MacDonald
authors: Department of Physics and Astronomy, University of California, Riverside, California 92521, USA.
authors: C N
authors: CN
authors: Lau