Multifunctional control of oxide interface via surface-oxygen-vacancy engineering

Abstract

Interfacial properties of oxide heterostructures, such as LaAlO3 (LAO)/SrTiO3 (STO), are closely related to the surface physicochemical states, offering unprecedented avenues for device tuning. Herein, we demonstrate that surface oxygen vacancy engineering through amorphous-LAO capping layer enables multifunctional control of interfacial conductivity, Kondo physics, and Rashba spin–orbit coupling at LAO/STO (001). X-ray photoelectron spectroscopy and electrical transport measurements reveal that the formation of oxygen vacancies at the LAO surface triggers charge transfer and insulator-to-metal transition of LAO/STO, with its carrier density increasing from 0.55 × 1013 to 1.08 × 1013 cm−2 as the amorphous-LAO thickness grows. The low-temperature resistance upturn exhibits Kondo effect characteristics, with Kondo temperature rising from 10.88 to 35.11 K concomitantly, accompanied by a two-orders-of-magnitude reduction in Kondo resistance, reflecting the transition of Kondo scattering center from Cr to Ti. Magnetotransport further reveals the enhancement of Rashba spin–orbital coupling with Rashba spin splitting energy Eso increasing from 2.54 to 4.07 meV and signature of Elliott–Yafet spin relaxation mechanism (spin–orbital relaxation time τso ∝ elastic scattering time τel), suggesting Cr ions as possible spin–orbit scattering impurities.