Theory for transport and temperature effects on two-photon photoemission: Application to Cu - art. no. 125122

Using a theory that treats on equal footing transport of excited electrons and electron-phonon scattering, we are able to explain the temperature depe ndence of the relaxation time in Cu as recently observed by Petek, Nagano, and Ogawa. We show that the unexpected increase of the relaxation time with temperature results from the drastic change of the electron motion due to the efficiency of electron-phonon scattering: the transport is ballistic at low temperature and becomes diffusive at room temperature. Finally, our th eory also reproduces the experimental measurements of the two-photon photoe mission intensity as a function of the pump-probe delay.