Strain Tunable Berry Curvature Dipole, Orbital Magnetization and Nonlinear Hall Effect in WSe2 Monolayer

TL;DR

This paper demonstrates how uniaxial strain in monolayer WSe2 induces a Berry curvature dipole, leading to an out-of-plane orbital magnetization and a nonlinear Hall effect, revealing new tunable topological transport phenomena.

Contribution

It experimentally shows strain-induced Berry curvature asymmetry in monolayer WSe2, enabling control of nonlinear Hall effects and out-of-plane orbital magnetization.

Findings

Strain breaks C3v symmetry, creating Berry curvature dipole in a single valley.

Emergent Berry curvature dipole causes quadratic nonlinear Hall response.

Orbital magnetization per current density reaches up to 60, promising for magnetic switching.

Abstract

The electronic topology is generally related to the Berry curvature, which can induce the anomalous Hall effect in time-reversal symmetry breaking systems. Intrinsic monolayer transition metal dichalcogenides possesses two nonequivalent K and K' valleys, having Berry curvatures with opposite signs, and thus vanishing anomalous Hall effect in this system. Here we report the experimental realization of asymmetrical distribution of Berry curvature in a single valley in monolayer WSe2 through applying uniaxial strain to break C3v symmetry. As a result, although the Berry curvature itself is still opposite in K and K' valleys, the two valleys would contribute equally to nonzero Berry curvature dipole. Upon applying electric field, the emergent Berry curvature dipole would lead to an out-of-plane orbital magnetization, which further induces an anomalous Hall effect with a linear response to E^2, known as nonlinear Hall effect. We show the strain modulated transport properties of nonlinear Hall effect in monolayer WSe2 with moderate hole-doping by gating. The second-harmonic Hall signals show quadratic dependence on electric field, and the corresponding orbital magnetization per current density can reach as large as 60. In contrast to the conventional Rashba-Edelstein effect with in-plane spin polarization, such current-induced orbital magnetization is along the out-of-plane direction, thus promising for high-efficient electrical switching of perpendicular magnetization.