Nonlinear Hall Effect in KTaO$_3$ Two-Dimensional Electron Gases

TL;DR

This paper reports the experimental observation of a nonlinear Hall effect in two-dimensional electron gases on KTaO$_3$ surfaces, demonstrating the influence of electric fields and crystal orientation on this symmetry-driven phenomenon.

Contribution

First experimental demonstration of nonlinear Hall effect in KTaO$_3$ 2DEGs, highlighting the role of Berry curvature and symmetry in non-magnetic materials.

Findings

Nonlinear Hall signal varies with surface orientation and electric field.

Transverse electric field modulates the nonlinear Hall response.

Results align with theoretical predictions of Berry curvature effects.

Abstract

The observation of a Hall effect, a finite transverse voltage induced by a longitudinal current, usually requires the breaking of time-reversal symmetry, for example through the application of an external magnetic field or the presence of long range magnetic order in a sample. Recently it was suggested that under certain symmetry conditions, the presence of finite Berry curvatures in the band structure of a system with time-reversal symmetry but without inversion symmetry can give rise to a nonlinear Hall effect in the presence of a probe current. In order to observe the nonlinear Hall effect, one requires a finite component of a so-called Berry dipole along the direction of the probe current. We report here measurements of the nonlinear Hall effect in two-dimensional electron gases fabricated on the surface of KTaO$_3$ with different surface crystal orientations as a function of the probe current, a transverse electric field and back gate voltage. For all three crystal orientations, the transverse electric field modifies the nonlinear Hall effect. We discuss our results in the context of the current understanding of the nonlinear Hall effect as well as potential experimental artifacts that may give rise to the same effects.