Scanning tunneling microscopy and spectroscopy on strong spin-orbit coupling chalcogenides*

A large number of A₂B₃ type chalcogenides with strong spin-orbit coupling like Bi₂Se₃, Bi₂Te₃, and Sb₂Te₃ etc. are topological insulators (TI) whereas Sb₂Se₃ is an exception in this group. In this talk, I will show, as the TI Bi₂Se₃, Sb₂Se₃ displays generation of highly spin-polarized current by point contact Andreev reflection spectroscopy. However, unlike in Bi₂Se₃, in case of Sb₂Se₃, a prominent quasiparticle interference (QPI) pattern could be observed in STM conductance mapping which contradicts the above experiment. According to the band structure calculation, there are two trivial surface states available and among them, one shows large splitting due to Rashba type spin-orbit coupling. In addition, we observe a large negative and anisotropic magnetoresistance in Sb₂Se₃. Experimental data reveal Sb₂Se₃ to be a trivial band insulator under ambient conditions with high spin-polarization due to Rashba type spin-orbit coupling.