Nonperturbative nonlinear transport in a topological semimetal

Ultrafast light-matter interaction can engineer topological responses in quantum materials via the creation of photon-dressed Floquet-Bloch states. Here, we report on the time-resolved transport properties of T_d-MoTe_2, a type-II Weyl semimetal, driven by a femtosecond pulse of mid-infrared laser light. Measurements were performed using an ultrafast optoelectronic device architecture based on laser-triggered photoconductive switches and waveguides. We observed a helicity-dependent injection current and an anomalous Hall effect, both of which scaled linearly with the applied laser field, in violation of the perturbative description of nonlinear optics and transport. Analysis of the results indicates that such nonperturbative nonlinear transport is a direct probe of the emergence and hybridization of Floquet-Bloch states. This work may provide deeper understanding toward programming technologically relevant responses in quantum materials with light.