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 non-equilibrium 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 metastable population at the bulk conduction band edge, which feeds a nonequilibrium population of the surface state persisting for >10 ps. 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.