title: Tunable moiré bands and strong correlations in small-twist-angle bilayer graphene.
abstract: According to electronic structure theory, bilayer graphene is expected to have anomalous electronic properties when it has long-period moiré patterns produced by small misalignments between its individual layer honeycomb lattices. We have realized bilayer graphene moiré crystals with accurately controlled twist angles smaller than 1° and studied their properties using scanning probe microscopy and electron transport. We observe conductivity minima at charge neutrality, satellite gaps that appear at anomalous carrier densities for twist angles smaller than 1°, and tunneling densities-of-states that are strongly dependent on carrier density. These features are robust up to large transverse electric fields. In perpendicular magnetic fields, we observe the emergence of a Hofstadter butterfly in the energy spectrum, with fourfold degenerate Landau levels, and broken symmetry quantum Hall states at filling factors ±1, 2, 3. These observations demonstrate that at small twist angles, the electronic properties of bilayer graphene moiré crystals are strongly altered by electron-electron interactions.
authors.affiliation: Microelectronics Research Center, Department of Electrical and Computer Engineering, The University of Texas at Austin, Austin, TX 78758.
authors.forename: Kyounghwan
authors.initials: K
authors.lastname: Kim
authors.affiliation: Department of Physics, The University of Texas at Austin, Austin, TX 78712.
authors.forename: Ashley
authors.initials: A
authors.lastname: DaSilva
authors.affiliation: Department of Physics, University of Arizona, Tucson, AZ 85721.
authors.forename: Shengqiang
authors.initials: S
authors.lastname: Huang
authors.affiliation: Microelectronics Research Center, Department of Electrical and Computer Engineering, The University of Texas at Austin, Austin, TX 78758.
authors.forename: Babak
authors.initials: B
authors.lastname: Fallahazad
authors.affiliation: Microelectronics Research Center, Department of Electrical and Computer Engineering, The University of Texas at Austin, Austin, TX 78758.
authors.forename: Stefano
authors.initials: S
authors.lastname: Larentis
authors.affiliation: National Institute for Materials Science, 1-1 Namiki Tsukuba Ibaraki 305-0044, Japan.
authors.forename: Takashi
authors.initials: T
authors.lastname: Taniguchi
authors.affiliation: National Institute for Materials Science, 1-1 Namiki Tsukuba Ibaraki 305-0044, Japan.
authors.forename: Kenji
authors.identifier: 0000-0003-3701-8119
authors.initials: K
authors.lastname: Watanabe
authors.affiliation: Department of Physics, University of Arizona, Tucson, AZ 85721; leroy@email.arizona.edu macd@physics.utexas.edu etutuc@mer.utexas.edu.
authors.forename: Brian J
authors.initials: BJ
authors.lastname: LeRoy
authors.affiliation: Department of Physics, The University of Texas at Austin, Austin, TX 78712; leroy@email.arizona.edu macd@physics.utexas.edu etutuc@mer.utexas.edu.
authors.forename: Allan H
authors.initials: AH
authors.lastname: MacDonald
authors.affiliation: Microelectronics Research Center, Department of Electrical and Computer Engineering, The University of Texas at Austin, Austin, TX 78758; leroy@email.arizona.edu macd@physics.utexas.edu etutuc@mer.utexas.edu.
authors.forename: Emanuel
authors.initials: E
authors.lastname: Tutuc
keywords: Hofstadter butterfly; graphene; moiré band; moiré crystal; twisted bilayer