  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.

Mesoscale and Nanoscale Physics