Emergent photovoltage on SmB6 surface upon bulk-gap evolution revealed by pump-and-probe photoemission spectroscopy

摘要

Recent studies suggest that an exemplary Kondo insulator SmB6 belongs to anew class of topological insulators (TIs), in which non-trivial spin-polarizedmetallic states emerge on surface upon the formation of Kondo hybridization gapin the bulk. Remarkably, the bulk resistivity reaches more than 20 Ohm cm at 4K, making SmB6 a candidate for a so-called bulk-insulating TI. We hereinvestigate optical-pulse responses of SmB6 by pump-and-probe photoemissionspectroscopy. Surface photovoltage effect is observed below ~90 K. Thisindicates that an optically-active band bending region develops beneath thenovel metallic surface upon the bulk-gap evolution. The photovoltaic effectpersists for >200 microsec, which is long enough to be detected by electronicsdevices, and could be utilized for optical gating of the novel metallicsurface.