Tracking quintuple layer oxidation on cleaved Bi2Se3 by optical second-harmonic anisotropy

Abstract

We find that the major and minor intensity lobes of a measured rotational-anisotropy pattern of optical second-harmonic generation (SHG) from a cleaved Bi2Se3 (111) surface can gradually change with time and eventually switch their relative amplitudes. This switching provides a means for tracking the progress of surface oxidation inside a quintuple layer of Bi2Se3. At different stages of oxidation, we perform pump-probe SHG experiments to study charge dynamics at the oxide/Bi2Se3 interface and to detect spin polarization of photoexcited surface states in the Bi2Se3 topological insulator.