Observation of the nonlinear anomalous Hall effect in 2D WTe₂

The Hall effect has been observed in systems with broken time reversal symmetry, such as the ordinary Hall effect in solids under a magnetic field and the anomalous Hall effect (AHE) in magnetic materials. Theories have indicated that in nonmagnetic materials with certain low crystal symmetries, a nonlinear Hall effect can be observed under zero magnetic field, in which the Hall voltage scales quadratically to the longitudinal current. Here we report an observation of such effect in atomically thin Td WTe2 flakes, a semimetal with only one mirror plane along the crystal b axis. In our angle-resolved electrical measurements, we observed a sinusoidal angular dependence of the nonlinear Hall effect, in which the effect maximizes when the driven current is perpendicular to the mirror plane and minimizes when it aligns to the mirror plane. This effect can be described as an anomalous Hall effect with a current induced magnetization. We further studied the temperature and doping dependence of the nonlinear hall conductivity. The result suggests that both intrinsic Berry curvature dipole and extrinsic spin-dependent scatterings contribute to the observed nonlinear AHE.