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

We analyze ultrafast electron dynamics in the time domain upon optical excitation of propagating surface plasmon-polaritons (SPs) in metal-dielectric heterostructures. Developing a kinetic model where both local and non-local electron relaxation in metals are included, we identify relevant timescales and extend the existing non-equilibrium electron dynamics framework onto the case of collective electronic excitations. The experimental data obtained in two distinct series of pump-probe measurements (with varied pump wavelength and angle of incidence) demonstrate SP-driven, one order of magnitude enhanced efficiency of the hot electron generation and the fourfold (up to 200 fs) slowdown of their non-local relaxation at the SP resonance. We discuss the perspectives of the SP-enabled manipulation of the non-equilibrium electron population lying at the crossover of photonics and ultrafast spintronics.