Dependence of nonequilibrium electron energy dynamics on electron-electron and electron-phonon interaction strengths

Photoexcitation of a metal results in hot electrons that cool on femto to picosecond time-scales because of electron-electron (e-e) and electron-phonon (e-p) interactions. In this talk, we report on the parametric dependence of the energy relaxation time on the ratio of e-e to e-p interactino strengths. We performed time-domain thermoreflectance, picosecond acoustic, and time-resolved magneto optical Kerr effect experiments to measure the hot electron energy relaxation time in various metals. We study Au (weak e-e interactions, weak e-p interactions), Al (weak e-e interactions, strong e-p interactions), Pd (strong e-e interactions, medium e-p interactions)and their alloys. We find that, for metals with strong e-e interactions like Pd, the two temperature model provides an accurate description of the dynamics. For metals with weak e-e interactions, the two-temperature model fails.