Dynamics of excited electrons in copper and ferromagnetic transition metals: Theory and experiment

Both theoretical and experimental results for the dynamics of photoexcited electrons at surfaces of Cu and the ferromagnetic transition metals Fe, Co, and Ni are presented. A model for the dynamics of excited electrons is dev eloped, which is based on the Boltzmann equation and includes effects of ph otoexcitation, electron-electron scattering, secondary electrons (cascade a nd Auger electrons), and transport of excited carriers out of the detection region. From this we determine the time-resolved two-photon photoemission (TR-2PPE). Thus a direct comparison of calculated relaxation times with exp erimental results by means of TR-2PPE becomes possible. The comparison indi cates that the magnitudes of the spin-averaged relaxation time tau and of t he ratio tau(up arrow) / tau(down arrow) Of majority and minority relaxatio n times for the different ferromagnetic transition metals result not only f rom density-of-states effects, but also from different Coulomb matrix eleme nts M. Taking M-Fe>M-Cu>M-Ni =M-Co we get reasonable agreement with experim ents.