Plasmon excitation in beryllium: inelastic x-ray scattering experiments and first-principlescalculations

Abstract

An experimental and theoretical study of collective electronic excitations in Be ispresented. The plasmon energy and linewidth were measured by means of inelastic x-rayscattering spectroscopy. Measurements were performed on a polycrystalline sample and ina broad range of momentum transfers within the plasmon excitation regime.Theoretical plasmon dispersion and its linewidth in the whole Brillouin zone werederived from ab initio evaluations of the electron density response function. Thecalculations were performed with full inclusion of the electron band structure within therandom-phase approximation. Good agreement of experimental plasmon energy andlinewidth dispersions with direction-averaged theoretical results in all investigatedq-range is obtained. We conclude that, in Be, the band structureeffects alone can account for the observed finite plasmon lifetime atq = 0, as well as for the linewidth dispersion in the long-wavelength domain.