Enhanced circular photogalvanic effect in oxide two-dimensional electron gas via photoelectric synergistic modulation

We report a giant enhancement of circular photogalvanic effect (CPGE) in the oxide two-dimensional electron gas at LaAlO₃/SrTiO₃ and LaAlO₃/KTaO₃ interfaces through the synergistic ultraviolet (UV) photoexcitation and electrostatic gating. The UV illumination generates high-density photocarriers by promoting valence-to-conduction band transitions, which simultaneously increase the Fermi wave vector k_F and Fermi energy E_F. Concurrently, the gate-induced oxygen vacancy migration toward the interface amplifies the Rashba spin-orbit coupling coefficient α_R. Strikingly, the CPGE photocurrent exhibits a nonmonotonic dependence on both gate voltage and UV intensity, peaking at an optimal carrier density where k_F and α_R cooperatively enhance the spin-momentum locking. This dual control strategy achieves a CPGE responsivity of 22.71 µV for LaAlO₃/KTaO₃ interfaces. Our findings establish the photoelectric coupling as a powerful knob for tailoring nonequilibrium spin phenomena in quantum oxide interfaces, with direct implications for reconfigurable spintronic devices.