Two-dimensional topological phases and electronic spectrum of Bi2Se3 thin films from GW calculations

We discuss topological and electronic properties of thin films of the topological insulator Bi2Se3 employing the GW method. We obtain a topologically trivial phase for films of one to six quintuple layers thickness, whereas a quantum spin Hall phase is observed in neither of these films. This challenges recent contradictory reports on quantum spin Hall phases in Bi2Se3 films from both theory and experiment. Moreover, we argue that one cannot conclude the topological phase from the band structures measured in those studies. The reliability of our results is supported by the excellent agreement of all calculated spectral features with photoemission experiments, i.e., the band gaps and the energy and slope of the Dirac state.