Driving materials with strong, periodic electromagnetic fields, known as Floquet engineering, is a powerful tool to manipulate the properties of quantum materials. Using circularly polarized light, artificial magnetic fields can be created in the photon-dressed Floquet-Bloch states that form. This mechanism, when applied to 3D Dirac and Weyl systems, is predicted to lead to photon-dressed movement of Weyl nodes which should be detectable in the transport sector. Using ultrafast transport methodology, we find direct evidence of transport from Floquet-Bloch states in the type-II Weyl semimetal T_d - MoTe_2 . In our measurements, we observed injection currents, and a helicity-dependent anomalous Hall effect whose scaling with laser field strongly deviate from the perturbative expectation of nonlinear optics. We show using Floquet theory that this discovery corresponds to the formation of a magnetic Floquet-Weyl semimetal state. Numerical ab initio simulations support this interpretation, indicating that the light-induced motion of the Weyl nodes contributes significantly to the measured transport signals. Moreover, from the amplitude of the light-induced anomalous Hall effect, we deduce that these photon-dressed states induce a large effective non-Maxwellian field (>30 T) during the drive.

In addition to modifying the topological transport properties during the field, we also discovered that mid-infrared light can efficiently excite coherent interlayer shear phonons which we can capture directly in the transport sector. We measure coherence between the phonon oscillation and the nonlinear Hall effect, which we interpret as an oscillation of the Weyl node positions in the Brillouin zone. This work is ongoing, but I will discuss both these results and the future of optical control over topology in quantum materials, including paths to persistent, dissipation free light-induced edge modes.