title: Composite fermions and broken symmetries in graphene.
abstract: The electronic properties of graphene are described by a Dirac Hamiltonian with a four-fold symmetry of spin and valley. This symmetry may yield novel fractional quantum Hall (FQH) states at high magnetic field depending on the relative strength of symmetry-breaking interactions. However, observing such states in transport remains challenging in graphene, as they are easily destroyed by disorder. In this work, we observe in the first two Landau levels the two-flux composite-fermion sequences of FQH states between each integer filling factor. In particular, the odd-numerator fractions appear between filling factors 1 and 2, suggesting a broken-valley symmetry, consistent with our observation of a gap at charge neutrality and zero field. Contrary to our expectations, the evolution of gaps in a parallel magnetic field suggests that states in the first Landau level are not spin-polarized even up to very large out-of-plane fields.
authors.affiliation: Department of Applied Physics, Stanford University, Stanford, California 94305, USA.
authors.forename: F
authors.initials: F
authors.lastname: Amet
authors.affiliation: Department of Physics, Stanford University, Stanford, California 94305, USA.
authors.forename: A J
authors.initials: AJ
authors.lastname: Bestwick
authors.affiliation: Department of Physics, Stanford University, Stanford, California 94305, USA.
authors.forename: J R
authors.initials: JR
authors.lastname: Williams
authors.affiliation: National High Magnetic Field Laboratory, Tallahassee, Florida 32310-3706, USA.
authors.forename: L
authors.initials: L
authors.lastname: Balicas
authors.affiliation: Advanced Materials Laboratory, National Institute for Materials Science, 1-1 Namiki, Tsukuba 305-0044, Japan.
authors.forename: K
authors.initials: K
authors.lastname: Watanabe
authors.affiliation: Advanced Materials Laboratory, National Institute for Materials Science, 1-1 Namiki, Tsukuba 305-0044, Japan.
authors.forename: T
authors.initials: T
authors.lastname: Taniguchi
authors.affiliation: 1] Department of Applied Physics, Stanford University, Stanford, California 94305, USA [2] Department of Physics, Stanford University, Stanford, California 94305, USA.
authors.forename: D
authors.initials: D
authors.lastname: Goldhaber-Gordon