Attosecond time-resolved streaking spectroscopy as a probe of strong field effects at the solid-vacuum interface of layered materials

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Strong electromagnetic fields in the vicinity of the solid-vacuum interface can dynamically change surface properties and might serve to control interfacial charge transfer processes on a sub-cycle time-scale. The implementation of such strong field control requires both, the complete knowledge of the actual field distribution on an atomic length scale and the understanding of the complex processes occurring in this massively perturbed many-body system. Presently the atomic-scale local dynamic field distribution in the vicinity of the interface is unknown. This issue is addressed in the present project that aims to improve the understanding of the fundamental processes governing the action of strong IR fields at interfaces and also addresses open questions concerning the dynamics of the photoemission process. To achieve these goals attosecond streaking spectroscopy at solid surfaces is employed. Photoelectrons excited by a single attosecond XUV pulse propagate through the substrate-vacuum interface and interact with the simultaneously present intense IR streaking field. The fundamental mechanisms and processes determining the observed delays in photoemission are still under debate and no complete theoretical model is available yet. In this project transition metal dichalcogenides forming layered van der Waals crystals and other layered materials are employed to localize the origin of the emitted core level photoelectrons with atomic precision. The experiments conducted up to now indicate that the photoelectron streaking is strongly affected by the atomic scale local field distribution close to the interface. Further experiments using such layered materials and single van der Waals crystal monolayers will provide a test of this working hypothesis. The systematic investigation of the angular dependence of the streaking effect shall provide essential information on the impact of local streaking fields.