Circular photogalvanic effect at the surface of hydrogenated perovskite oxides

Abstract

Surface electronic states represent a crucial material system for both fundamental physics research and electronic device applications. In this study, the circular photogalvanic effect (CPGE) in hydrogenated surface states was systematically investigated. Both hydrogenated SrTiO3 and KTaO3 exhibited significant photocurrents under 780, 532, and 450 nm illumination, demonstrating strong spin–orbit coupling (SOC) at the surface states. X-ray photoelectron spectroscopy measurements revealed a hydrogen density gradient near the surface, which breaks inversion symmetry and consequently induces strong SOC. The nonzero CPGE photocurrent under normal incidence and its incidence angle dependence suggest the Cs symmetry of hydrogenated SrTiO3, which can be attributed to the anisotropic hydrogen distribution within the crystal lattice.