Observation of unoccupied states of SnTe(111) using pump-probe ARPES measurement

Abstract

A IV-VI compound SnTe is proposed to be a topological crystalline insulator (TCI), and the band structures have been studied by using angle-resolved photoemission spectroscopy (ARPES). However, the topological surface states (TSSs) that hallmark the nontrivial topology disperse mostly in the unoccupied side where access via ARPES is limited. Here we investigate the (111) face of a SnTe film by using pump-probe ARPES. We find distinct energy sections in the unoccupied side that behave differently in terms of the excitation and recovery dynamics. From these different behaviors, the boundaries of these sections are attributed to the edges of the conduction and valence bands. High statistics data reveal that the TSSs are traversing the band gap, which evidences that SnTe belongs to a TCI. We also find that the bulk bands near the gap show splitting, which is attributed to the Rashba effect occurring in the dipolar surface region.