Electron dynamics of unoccupied states in topological insulators

Abstract The topological insulators Bi 2 Se 3 and Bi 2 Te 2 Se have been shown to possess unoccupied topological surface states at the center of the surface Brillouin zone at energies around 1.3 eV above the Fermi level. Using time-resolved two-photon photoemission we study the electron dynamics of the unoccupied topological surface states, image-potential states and conduction bands on these surfaces.