The Interplay of Topological Surface and Bulk Electronic States in Bi2Se3

In this Letter 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 bulk-like states with small amplitudes at the surface. The topological surface states coexist with bulk-like 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 bulk-like surface states.