Nonlinear transport and optical responses in atomically thin WTe₂

Many exotic quantum phenomena of today’s forefront materials arise from the interplay among symmetry, topology, quantum geometry and correlations. Therefore, their detection and characterization require one to probe multiple aspects of the materials. We demonstrate nonlinear electrical transport and infrared optoelectronic measurements as symmetry sensitive probes of the low energy electron states in novel metals/semimetals. Using monolayer and bilayer WTe₂ as examples, I will show how nonlinear electrical transport and infrared photocurrent can reveal the Berry curvature properties in a highly symmetry sensitive way. In particular, the nonlinear electrical transport in bilayer WTe₂ uncovers a new type of Hall effect, the nonlinear Hall effect. Interestingly, this is an electrical Hall effect in a nonmagnetic material and in the absence of external magnetic field. Coupled with the gate tunability of 2D materials, we demonstrate that such nonlinear Hall effect provides a powerful tool to detect the Berry curvature of nonmagnetic quantum materials in an energy-resolved way.