title: Evidence for a fractional fractal quantum Hall effect in graphene superlattices.
abstract: The Hofstadter energy spectrum provides a uniquely tunable system to study emergent topological order in the regime of strong interactions. Previous experiments, however, have been limited to low Bloch band fillings where only the Landau level index plays a role. We report measurements of high-mobility graphene superlattices where the complete unit cell of the Hofstadter spectrum is accessible. We observed coexistence of conventional fractional quantum Hall effect (QHE) states together with the integer QHE states associated with the fractal Hofstadter spectrum. At large magnetic field, we observed signatures of another series of states, which appeared at fractional Bloch filling index. These fractional Bloch band QHE states are not anticipated by existing theoretical pictures and point toward a distinct type of many-body state.
authors.affiliation: Department of Mechanical Engineering, Columbia University, New York, NY 10027, USA. Kavli Institute at Cornell for Nanoscale Science, Ithaca, NY 14853, USA.
authors.forename: Lei
authors.initials: L
authors.lastname: Wang
authors.affiliation: Department of Mechanical Engineering, Columbia University, New York, NY 10027, USA.
authors.forename: Yuanda
authors.initials: Y
authors.lastname: Gao
authors.affiliation: Department of Physics, Columbia University, New York, NY 10027, USA.
authors.forename: Bo
authors.initials: B
authors.lastname: Wen
authors.affiliation: Department of Physics, Columbia University, New York, NY 10027, USA.
authors.forename: Zheng
authors.initials: Z
authors.lastname: Han
authors.affiliation: National Institute for Materials Science, 1-1 Namiki, Tsukuba 305-0044, Japan.
authors.forename: Takashi
authors.initials: T
authors.lastname: Taniguchi
authors.affiliation: National Institute for Materials Science, 1-1 Namiki, Tsukuba 305-0044, Japan.
authors.forename: Kenji
authors.initials: K
authors.lastname: Watanabe
authors.affiliation: Department of Physics, Tohoku University, Sendai 980-8578, Japan.
authors.forename: Mikito
authors.initials: M
authors.lastname: Koshino
authors.affiliation: Department of Mechanical Engineering, Columbia University, New York, NY 10027, USA.
authors.forename: James
authors.initials: J
authors.lastname: Hone
authors.affiliation: Department of Physics, Columbia University, New York, NY 10027, USA. cdean@phys.columbia.edu.
authors.forename: Cory R
authors.initials: CR
authors.lastname: Dean