Ultrafast Optical Excitation of a Persistent Surface-State Population in   the Topological Insulator Bi2Se3
  Using femtosecond time- and angle- resolved photoemission spectroscopy, we investigated the nonequilibrium dynamics of the topological insulator Bi2Se3. We studied p-type Bi2Se3, in which the metallic Dirac surface state and bulk conduction bands are unoccupied. Optical excitation leads to a meta-stable population at the bulk conduction band edge, which feeds a nonequilibrium population of the surface state persisting for >10ps. This unusually long-lived population of a metallic Dirac surface state with spin texture may present a channel in which to drive transient spin-polarized currents. 
Jonathan A. Sobota, Shuolong Yang, James G. Analytis, Yulin Chen, Ian   R. Fisher, Patrick S. Kirchmann, Z.-X. Shen
cond-mat.mtrl-sci cond-mat.mes-hall