Ultrafast transport and relaxation of hot plasmonic electrons in metal-dielectric heterostructures

摘要： Owing to the ultrashort timescales of ballistic electron transport, relaxation dynamics of hot nonequilibrium electrons is conventionally considered local. Utilizing propagating surface plasmon-polaritons (SPs) in metal-dielectric heterostructures, we demonstrate that both local (relaxation) and nonlocal (transport) hot electron dynamics contribute to the transient optical response. The data obtained in two distinct series of pump-probe experiments demonstrate a strong increase in both nonthermal electron generation ef?ciency and nonlocal relaxation timescales at the SP resonance. We develop a simple kinetic model incorporating a SP excitation, where both local and nonlocal electron relaxation in metals are included, and analyze nonequilibrium electron dynamics in its entirety in the case of collective electronic excitations. Our results elucidate the role of SPs in nonequilibrium electron dynamics and demonstrate rich perspectives of ultrafast plasmonics for tailoring spatiotemporal distribution of hot electrons in metallic nanostructures.