Resonant Non-Linear Photocurrent in Type-II Weyl Semimetal WP2

Weyl semimetals are topological systems that have generated considerable interest due to their transport properties as well as their nonlinear response to light. Due to the topological nature of the Weyl cones, these systems are very sensitive to nonlinear responses such as the shift and injection current response to polarized light. Optical experiments done on various Weyl semimetals have already shown large photocurrent responses, but so far investigation into enhancement of nonlinear responses due to excitations from the Weyl node has been quite limited. These measurements are experimentally difficult due to the low energy requirement to excite about the node, however excitations between Weyl nodes and the Fermi surface may be a way to avoid this challenge. Here we report on mid-IR photocurrent measurements performed on the type-II Weyl semimetal WP2. Polarization and wavelength dependence of the response shows a room temperature injection current response resonant with the energy of one of the Weyl nodes.