Spatial Distribution of Topological Surface State Electrons in Bi₂Te₃ Probed by Low Energy Na⁺ Ion Scattering

Bi₂Te₃ is a topological insulator (TI) whose unique properties result from topological surface states (TSS) in the band gap. The TSS are responsible for the novel spin-dependent transport properties of TI materials and their detailed characterization is needed to completely understand the relevant physics. DFT calculations suggest that the TSS electrons accumulate locally below the surface Te atoms and above the 2^nd layer Bi atoms, which would create upward pointing surface dipoles at the Te sites and downward pointing dipoles at the Bi sites. The neutralization probability of scattered low energy alkali ions depends on the surface local electrostatic potential (LEP) directly above the scattering site, and is thus particularly sensitive to dipoles that induce inhomogeneities in the local surface potential. It is found that the neutralization is larger when scattered from Te than from Bi, experimentally confirming the presence of the dipoles and thereby the spatial distribution of the conductive electrons in the TSS.