Photogalvanic effect in Weyl semimetals

We theoretically study the impact of impurities on the photogalvanic effect (PGE) in Weyl semimetals with weakly tilted Weyl cones. Our calculations are based on a two-nodes model with an inversion symmetry breaking offset and we employ a kinetic equation approach in which both optical transitions as well as particle-hole excitations near the Fermi energy can be taken into account. We focus on the parameter regime with a single photoactive node and control the calculation in small impurity concentration. Internode scattering is treated generically and therefore our results allow us to continuously interpolate between the cases of short-range and long-range impurities. We find that the time evolution of the circular PGE may be nonmonotonic for intermediate internode scattering. Furthermore, we show that the tilt vector introduces three additional linearly independent components to the steady-state photocurrent. Amongst them, the photocurrent in direction of the tilt takes a particular role inasmuch it requires elastic internode scattering or inelastic intranode scattering to be relaxed. It may therefore be dominant. The tilt also generates skew scattering which leads to a current component perpendicular to both the incident light and the tilt. We extensively discuss our findings and comment on the possible experimental implications.