We report on angle-resolved photoemission spectroscopic studies on a parent topological insulator, ${\text{Bi}}_2{\text{Se}}_3$. The linewidth of the spectral function (inverse of the quasiparticle lifetime) of the topological metallic states shows an anomalous behavior. This behavior can be reasonably accounted for by assuming the decay of the quasiparticles predominantly into bulk electronic states through electron-electron interaction and defect scattering. Studies on aged surfaces reveal that topological metallic states are very much unaffected by the potentials created by adsorbed atoms or molecules on the surface, indicating that topological states could be indeed protected against weak perturbations.

• Received 25 November 2009

DOI:https://doi.org/10.1103/PhysRevB.81.041405