Dynamics of Excited Electrons in Copper and Ferromagnetic Transition Metals: Theory and Experiment

TL;DR

This paper presents a combined theoretical and experimental study of excited electron dynamics in copper and ferromagnetic transition metals, developing a model based on the Boltzmann equation to interpret time-resolved photoemission data.

Contribution

It introduces a comprehensive model for excited electron dynamics that accounts for various scattering processes and transport, enabling direct comparison with experimental TR-2PPE results.

Findings

Relaxation times depend on density-of-states and Coulomb matrix elements.

The model achieves reasonable agreement with experimental relaxation times.

Differences in Coulomb matrix elements influence spin-dependent relaxation.

Abstract

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 developed, which is based on the Boltzmann equation and includes effects of photoexcitation, electron-electron scattering, secondary electrons (cascade and 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 experimental results by means of TR-2PPE becomes possible. The comparison indicates that the magnitudes of the spin-averaged relaxation time \tau and of the ratio \tau_\uparrow/\tau_\downarrow of majority and minority relaxation times for the different ferromagnetic transition metals result not only from density-of-states effects, but also from different Coulomb matrix elements M. Taking M_Fe > M_Cu > M_Ni = M_Co we get reasonable agreement with experiments.