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 <a:math xmlns:a="http://www.w3.org/1998/Math/MathML"> <a:mrow> <a:msub> <a:mi>LaAlO</a:mi> <a:mn>3</a:mn> </a:msub> <a:mo>/</a:mo> <a:msub> <a:mi>SrTiO</a:mi> <a:mn>3</a:mn> </a:msub> </a:mrow> </a:math> and <b:math xmlns:b="http://www.w3.org/1998/Math/MathML"> <b:mrow> <b:mi>LaAl</b:mi> <b:msub> <b:mi mathvariant="normal">O</b:mi> <b:mn>3</b:mn> </b:msub> </b:mrow> <b:mo>/</b:mo> <b:mrow> <b:mi>KTa</b:mi> <b:msub> <b:mi mathvariant="normal">O</b:mi> <b:mn>3</b:mn> </b:msub> </b:mrow> </b:math> 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 <e:math xmlns:e="http://www.w3.org/1998/Math/MathML"> <e:msub> <e:mi>k</e:mi> <e:mi mathvariant="normal">F</e:mi> </e:msub> </e:math> and Fermi energy <g:math xmlns:g="http://www.w3.org/1998/Math/MathML"> <g:msub> <g:mi>E</g:mi> <g:mi mathvariant="normal">F</g:mi> </g:msub> </g:math> . Concurrently, the gate-induced oxygen vacancy migration toward the interface amplifies the Rashba spin-orbit coupling coefficient <i:math xmlns:i="http://www.w3.org/1998/Math/MathML"> <i:msub> <i:mi>α</i:mi> <i:mi mathvariant="normal">R</i:mi> </i:msub> </i:math> . Strikingly, the CPGE photocurrent exhibits a nonmonotonic dependence on both gate voltage and UV intensity, peaking at an optimal carrier density where <k:math xmlns:k="http://www.w3.org/1998/Math/MathML"> <k:msub> <k:mi>k</k:mi> <k:mi mathvariant="normal">F</k:mi> </k:msub> </k:math> and <m:math xmlns:m="http://www.w3.org/1998/Math/MathML"> <m:msub> <m:mi>α</m:mi> <m:mi mathvariant="normal">R</m:mi> </m:msub> </m:math> cooperatively enhance the spin-momentum locking. This dual control strategy achieves a CPGE responsivity of 22.71 µV for <o:math xmlns:o="http://www.w3.org/1998/Math/MathML"> <o:mrow> <o:mi>LaAl</o:mi> <o:msub> <o:mi mathvariant="normal">O</o:mi> <o:mn>3</o:mn> </o:msub> </o:mrow> <o:mo>/</o:mo> <o:mrow> <o:mi>KTa</o:mi> <o:msub> <o:mi mathvariant="normal">O</o:mi> <o:mn>3</o:mn> </o:msub> </o:mrow> </o:math> 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.