%0 Journal Article
%T Direct Optical Coupling to an Unoccupied Dirac Surface State in the Topological Insulator Bi$_2$Se$_3$
%A Jonathan A. Sobota
%A Shuolong Yang
%A Alexander F. Kemper
%A J. J. Lee
%A Felix T. Schmitt
%A Wei Li
%A Robert G. Moore
%A James G. Analytis
%A Ian R. Fisher
%A Patrick S. Kirchmann
%A Thomas P. Devereaux
%A Zhi-Xun Shen
%J Physics
%D 2013
%I arXiv
%R 10.1103/PhysRevLett.111.136802
%X We characterize the occupied and unoccupied electronic structure of the topological insulator Bi$_2$Se$_3$ 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.
%U http://arxiv.org/abs/1309.1405v1