21.

Bulk quantum geometric photocurrents. (a,b) Injection (a) and shift photocurrents (b) arise from the change in electron group velocity (v _c and v _v in the conduction and valence bands) and real space displacement (R _c and R _v in conduction and valence bands) when electrons are photoexcited from valence to conduction bands in noncentrosymmetric materials. (c−e) In the presence of a Fermi surface, a variety of other mechanisms become activated including (c) an intrinsic Fermi surface effect (arising from virtual interband processes), (d) a Berry curvature dipole (inset; asymmetric distribution of Berry curvature across a Fermi surface), and (e) skew scattering contributions (produced when the transition rates W between Bloch states at momenta k _1,2 become imbalanced). These mechanisms provide a means for achieving a type of optoelectronics based on bulk noncentrosymmetric metals.