Nonlinear circular dichroism reveals the local Berry curvature

Abstract The transfer of angular momentum between light and crystalline solids during nonlinear optical processes is typically interpreted in terms of angular momentum conservation and the rotational symmetry of the crystal lattice. However, these cornerstone principles rely on macroscopic symmetry arguments, providing little insight into the microscopic origin of angular momentum transfer. Here we show that changes in the spin angular momentum of light in high-harmonic generation processes, which we probe via nonlinear circular dichroism, are directly proportional to the local Berry curvature at a single optical resonance, therefore establishing a link between nonlinear light–matter interactions and the quantum geometry of electronic states. We demonstrate this relationship using second-harmonic generation in monolayer WSe 2 , using circularly polarized light to break time-reversal symmetry and lift the degeneracy between the valleys. The resulting second-harmonic circular dichroism can be controlled through the intensity and helicity of the circularly polarized light, hence offering a method for the control and readout of the optically probed Berry curvature.