title: Direct optical coupling to an unoccupied dirac surface state in the topological insulator Bi2Se3.
abstract: We characterize the occupied and unoccupied electronic structure of the topological insulator Bi2Se3 by one-photon and two-photon angle-resolved photoemission spectroscopy and slab band structure calculations. We reveal a second, unoccupied Dirac surface state with similar electronic structure and physical origin to the well-known topological surface state. This state is energetically located 1.5 eV above the conduction band, which permits it to be directly excited by the output of a Ti:sapphire laser. This discovery demonstrates the feasibility of direct ultrafast optical coupling to a topologically protected, spin-textured surface state.
authors.affiliation: SLAC National Accelerator Laboratory, Stanford Institute for Materials and Energy Sciences, 2575 Sand Hill Road, Menlo Park, California 94025, USA and Department of Applied Physics, Geballe Laboratory for Advanced Materials, Stanford University, Stanford, California 94305, USA and Department of Physics, Stanford University, Stanford, California 94305, USA.
authors.forename: J A
authors.initials: JA
authors.lastname: Sobota
authors.forename: S-L
authors.initials: SL
authors.lastname: Yang
authors.forename: A F
authors.initials: AF
authors.lastname: Kemper
authors.forename: J J
authors.initials: JJ
authors.lastname: Lee
authors.forename: F T
authors.initials: FT
authors.lastname: Schmitt
authors.forename: W
authors.initials: W
authors.lastname: Li
authors.forename: R G
authors.initials: RG
authors.lastname: Moore
authors.forename: J G
authors.initials: JG
authors.lastname: Analytis
authors.forename: I R
authors.initials: IR
authors.lastname: Fisher
authors.forename: P S
authors.initials: PS
authors.lastname: Kirchmann
authors.forename: T P
authors.initials: TP
authors.lastname: Devereaux
authors.forename: Z-X
authors.initials: ZX
authors.lastname: Shen