Spatially Dispersive Circular Photogalvanic Effect in Weyl Semimetals

We observe a circulating photocurrent in type-II Weyl semimetals MoTe₂/Mo_0.9W_0.1Te₂, driven by circularly polarized light at normal incidence. This effect occurs exclusively in the Weyl phase and crucially we find that it is associated with a spatially inhomogeneous beam profile. We assign this response to spatially dispersive contribution to the circular photogalvanic effect (s-CPGE). We systematically analyze the microscopic mechanism of this photocurrent by calculating the quantum density matrix to first order in spatial gradients and second order in the electric field. We find that the observed s-CPGE is dominated by terms in the response function that are non-zero only in the inversion broken Weyl phase. We demonstrate our finding by numerical calculations of its frequency dependence using a minimal model of an inversion broken Weyl semimetal and use the calculation to find low and high frequency scaling behavior of the photocurrent.