Dielectric screening in electromagnetic dressing of semiconductors

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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, electromagnetic dressing can also occur for quasifree electrons outside the material, giving rise to so-called Volkov states. In certain cases, most notably in metallic systems, strong surface screening reduces the penetration of the driving electromagnetic field into the solid, resulting in Volkov contributions that dominate over Floquet ones. This underscores the importance of carefully accounting for the material's dielectric response when analyzing the origin of light-induced band replicas using time- and angle-resolved photoemission spectroscopy. 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 2 H − 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 function. The extracted values typically lie between the reported dielectric constants for monolayer and bulk crystals. Furthermore, we demonstrate that increasing the pump fluence of the infrared pump laser enables the generation of high-order Volkov sidebands, which exhibit clear signatures of nonlinear light-matter interactions in their temporal dynamics, polarization dependence, and angular distributions. Finally, we show that for our experimental geometry, the quasitransparent nature of semiconductors in the below-band-gap driving regime allows the optical pump to propagate within the sample and undergo multiple total internal reflections. This process produces a series of temporally delayed Volkov replicas in pump-probe measurements via electromagnetic dressing of photoelectrons by the evanescent field associated with total internal reflections. Together, these systematic studies uncover several previously unexplored aspects of Floquet-Volkov dressing in solids, highlighting the central role of dielectric screening of the driving field.
Funding Information
  • Agence Nationale de la Recherche (ANR-23-EXLU-0002)
  • Agence Nationale de la Recherche (ANR-23-EXLU-0004)
  • European Research Council (ERC-2022-STG)
  • European Research Council (101076639)
  • H2020 Marie Skłodowska-Curie Actions (101198277)
  • H2020 Marie Skłodowska-Curie Actions (HORIZON-MSCA-2023-DN-01 101169225)

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