Strain Tunable Berry Curvature Dipole, Orbital Magnetization and Nonlinear Hall Effect in WSe<sub>2</sub> Monolayer*
Mao-Sen Qin, Peng-Fei Zhu, Xing-Guo Ye, Wen-Zheng Xu, Zhen-Hao Song, Jing Liang, Kaihui Liu, Zhi-Min Liao
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 WSe 2 via applying uniaxial strain to break C 3 v 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 E , the emergent Berry curvature dipole D would lead to an out-of-plane orbital magnetization M ∝ D ⋅ E , 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 WSe 2 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 M / J 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.