Scanning Tunneling Microscopy and Spectroscopy of Topological Insulators

We performed cryogenic scanning tunneling microscopy and spectroscopy measurements of the surface and defect states in topological insulators Bi2Se3 and Bi2Te3. Our measurements demonstrate gapless surface states in both materials. While Bi2Te3 is naturally p-doped, we observed both p- and n-doped regions on the cleaved surface. These observations can be correlated with local cleaving within quintuple layers seen from topography measurements, suggesting a new route for surface doping of topological insulators. We also describe unique clover-shaped defects states appearing inside the bulk valence band. Our band structure calculations show that these states originate from a combination of bonding anisotropy and surface band bending, resulting in formation of subsurface resonances.