Lifetimes and mean-free paths of hot electrons in the alkali metals

We report first principle calculations of electron and hole inelastic lifetimes for alkali metals (Na and K) within the framework of the GW approximation of many-body theory. The results show that at low energies the lifetimes are slightly smaller than prediction of a free-electron model, and that there is no noticeable momentum-direction dependence. We also look at the inelastic mean-free path λ, and conclude that the observed drops at a few eV in λ for the alkali elements with a strong d-band character cannot be attributed to the effect of these d bands in the lifetime, but to a crossover behavior of the velocity of the photoelectron.