Interplay of topological surface and bulk electronic states in Bi ₂Se₃

In this paper we present scanning tunneling microscopy density-of-states measurements and electronic structure calculations of the topological insulator Bi₂Se₃. The measurements show significant background states in addition to the expected Dirac cone. Density-functional calculations using a slab model and analysis of the partial density of states show that the background is consistent with bulklike states with small amplitudes at the surface. The topological surface states coexist with bulklike states in the valence band, appearing as a shoulder in the projected band structure. These results strongly support the picture suggested by recent scattering experiments of the quantum interference of topological and bulklike surface states.