Lifetimes of low-energy electron excitations in metals

We report theoretical studies of electron and hole lifetimes in a free-electron gas as well as in real metals Al and Nb by means of the ab initio many-body method and semi-empirical scattering theory approach. We show that for free-electron-like excitations a simple density-of-state convolution model of the scattering theory approach (STA-DOS) is a good approximation to the ab initio lifetimes, the energy dependence of the STA-DOS transition matrix element being rather unimportant. The approximation of energy-independent matrix element appears to also be reasonable for Nb. A good correspondence between the STA-DOS and ab initio momentum-averaged results is achieved for Nb with an adjusted matrix element, although the ab initio lifetimes disperse,greatly with respect to the averaged value.