STM Studies of Transport Properties of Topological Insulators

Strong spin-orbit coupling (SOC) can induce a novel insulating state (topological insulators or TIs) with metallic surface states that have a linear band dispersion of massless Dirac Fermions with spin-helicity. Quasi-particle interference (QPI) patterns from scanning tunneling microscopy and spectroscopy reveal that electrons in the surface states are spin-textured. A consequence is that back-scattering of a surface electron by non-magnetic impurities is strongly suppressed as predicted by the spin selection rule. In addition, the band dispersion of the non-trivial surface states obtained from dI/dV spectra in a magnetic field coincides with ARPES results. These results suggest that TIs can provide fertile grounds to study electron-spin interactions at the nano-scale as magnetic impurities enable spin-flip back-scattering and open up gaps by destroying the time-reversal symmetry.