Robust purely optical signatures of Floquet-Bloch states in crystals

Abstract: Strong light-matter interactions enable triggering on-demand novel functionalities in materials. For periodically driven solids, the Floquet-Bloch states have emerged as the natural states to characterize the physical properties of these non-equilibrium systems. However, robust signatures of the Floquet-Bloch states are needed as common experimental conditions, such as pulsed laser excitation and dissipative many-body dynamics can disrupt their formation and survival. Here, we identify a tell-tale signature of Floquet-Bloch states in the linear optical response of laser-dressed solids that remains prominent even in the presence of strong spectral congestion of bulk matter. To do so, we introduce a computationally efficient strategy to finally capture the response properties of realistic laser-dressed solids, and use it to compute the optical absorption of ZnO using a model of full-dimensionality. The computations reveal intense, spectrally isolated, absorption/stimulated emission features at mid-infrared energies present for a wide range of laser-driving conditions that arise due to the hybridization of the Floquet-Bloch states. As such, these spectral features open a purely optical pathway to investigate the birth and survival of Floquet-Bloch states while avoiding the experimental challenges of fully reconstructing the band structure.