Light-Induced Giant Enhancement of the Nonlinear Hall Effect in Two-Dimensional Electron Gases at KTaO₃ (111) Interfaces.

Abstract

The nonlinear Hall effect (NLHE), an emergent phenomenon in noncentrosymmetric systems, enables the generation of a transverse voltage without an external magnetic field through a second-order electrical response. However, achieving a sizable NLHE signal remains a critical challenge for its application in frequency-doubling and rectifying devices. Here, we report a light-induced giant enhancement of the NLHE in the 2D electron gas (2DEG) at the CaZrO₃/KTaO₃ (111) interface. Under illumination, the second harmonic Hall voltage increases substantially and undergoes a sign reversal. Correspondingly, the second-order transverse conductivity (σ(2) yxx) increases by nearly five orders of magnitude, reaching 2.4 µm V^-1 Ω^-1, while also reversing its sign. Scaling analysis identifies skew scattering as the dominant mechanism, which is highly tunable via optical gating. Photoexcitation pumps electrons from in-gap states into the Ta 5d conduction band, generating high-mobility photocarriers that increase the cubic scattering time (τ³) and thereby, dramatically boost σ(2) yxx. First-principles calculations further reveal that the Berry curvature triple changes sign as the Fermi level approaches the higher-lying L_z,+ subbands, in the Ta 5d accounting for the observed sign reversal. Our work offers a new strategy to optically control the NLHE in oxide 2DEG systems, highlighting the tunability of nonlinear transport by optical excitation.