Nonequilibrium electron dynamics in noble metals

Electron-electron and electron-lattice interactions in noble metals are dis cussed in the light of two-color femtosecond pump-probe measurements in sil ver films. The internal thermalization of a nonequilibrium electron distrib ution created by intraband absorption of a pump pulse is followed by probin g the induced optical property changes in the vicinity of the frequency thr eshold for the d band to Fermi surface transitions. This is shown to take p lace with a characteristic time constant of 350 fs, significantly shorter t han previously reported In gold. This difference is ascribed to a weaker sc reening of the electron-electron interaction by the d-band electrons in sil ver than in gold. These results are in quantitative agreement with numerica l simulations of the electron relaxation dynamics using a reduced static sc reening of the electron-electron Coulomb interaction, and including bound e lectron screening. Electron-lattice thermalization has been studied using a probe frequency out of resonance with the interband transitions. In both m aterials, the transient nonthermal nature of the electron distribution lead s to the observation of a short-time delay reduction of the energy-loss rat e of the electron gas to the lattice, in very good agreement with our theor etical model.