Focused surface plasmon polaritons coherently couple to electronic states in above-threshold electron emission

Abstract When an intense light field strongly interacts with the band structure of a solid, formation hybrid light-matter quantum states becomes possible. Examples such Floquet-Bloch have been reported, but engineering using Floquet can suffer from dissipation and decoherence. Sustaining necessary coherence interactions requires robust electronic in combination strong fields suitable polarization frequency. Here, we explore coherent coupling nano-focused surface plasmon polaritons (SPP) to distinct solid. We observe above-threshold electron emission Au(111) Shockley state by absorption up seven SPP quanta. Using time-resolved photoelectron spectroscopy interaction SPPs during is investigated process shown be similar light-driven above threshold emission. Ultimately, our work could render SPP-based nano-optical systems feasible.