  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.
