Quantum geometry induced second harmonic generation

Abstract: Quantum geometry of the electron wave function plays a significant role in the linear and non-linear responses of crystalline materials. Here, we study quantum geometry induced second harmonic generation. We identify non-linear responses stemming from the quantum geometric tensor and the quantum geometric connection in systems with finite Fermi surfaces and disorder. In addition to the injection, shift, and anomalous currents we find two new contributions, which we term double resonant and higher-order pole contributions. Our findings can be tested in state-of-the-art devices in WTe2 (time-reversal symmetric system) and in CuMnAs (parity-time reversal symmetric systems).