Dielectric Screening in Floquet-Volkov Dressing of Semiconductors

Abstract: Nonequilibrium manipulation of quantum materials via electromagnetic dressing provides an on-demand route to tailoring electronic band structures through Floquet engineering. Time- and angle-resolved photoemission spectroscopy offers a direct means to probe these light-dressed electronic states. In such photoemission experiments, dressing can also occur for quasi-free electrons outside the material, giving rise to Volkov states. In certain cases, strong surface screening reduces the penetration of the driving field into the solid, resulting in Volkov contributions that dominate over Floquet ones. In this work, we systematically investigate the influence of materials' dielectric properties on Floquet-Volkov dressing of semiconductors, focusing on bulk layered van der Waals materials GeS, SnS, and 2H-WSe$_2$. First, by combining a simple model based on Fresnel equations with an electron-scattering description of Volkov amplitudes, we use polarization-dependent Volkov sideband intensities to extract a lower bound for the real part of the materials' dielectric functions, which typically lie between the reported dielectric constants for monolayer and bulk crystals. We demonstrate that increasing the fluence of the pump laser enables the generation of high-order Volkov sidebands which exhibit clear signatures of nonlinear light-matter interactions. Finally, we show that for our experimental geometry, the quasi-transparent nature of semiconductors in below-band-gap driving regime allows the optical pump to propagate within the sample and undergo multiple total internal reflections, producing temporally delayed Volkov replicas in pump-probe measurements via dressing of photoelectrons by evanescent fields. These systematic studies uncover previously unexplored aspects of Floquet-Volkov dressing in solids, highlighting the role of dielectric screening of the driving field.