title: Charge Inversion and Topological Phase Transition at a Twist Angle Induced van Hove Singularity of Bilayer Graphene.
abstract: van Hove singularities (VHS's) in the density of states play an outstanding and diverse role for the electronic and thermodynamic properties of crystalline solids. At the critical point the Fermi surface connectivity changes, and topological properties undergo a transition. Opportunities to systematically pass a VHS at the turn of a voltage knob and study its diverse impact are however rare. With the advent of van der Waals heterostructures, control over the atomic registry of neighboring graphene layers offers an unprecedented tool to generate a low energy VHS easily accessible with conventional gating. Here we have addressed magnetotransport when the chemical potential crosses the twist angle induced VHS in twisted bilayer graphene. A topological phase transition is experimentally disclosed in the abrupt conversion of electrons to holes or vice versa, a loss of a nonzero Berry phase and distinct sequences of integer quantum Hall states above and below the singularity.
authors.affiliation: Max-Planck-Institut für Festköperforschung , 70569 Stuttgart, Germany.
authors.forename: Youngwook
authors.initials: Y
authors.lastname: Kim
authors.affiliation: Max-Planck-Institut für Festköperforschung , 70569 Stuttgart, Germany.
authors.forename: Patrick
authors.initials: P
authors.lastname: Herlinger
authors.affiliation: New York University , Shanghai 200120, China.|NYU-ECNU Institute of Physics at NYU Shanghai , Shanghai 200062, China.
authors.forename: Pilkyung
authors.initials: P
authors.lastname: Moon
authors.affiliation: Department of Physics, Tohoku University , Sendai 980-8578, Japan.
authors.forename: Mikito
authors.initials: M
authors.lastname: Koshino
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: Max-Planck-Institut für Festköperforschung , 70569 Stuttgart, Germany.
authors.forename: Jurgen H
authors.initials: JH
authors.lastname: Smet
keywords: Moiré superlattice; Twisted bilayer graphene; topological transition; van Hove singularity