Electron-density dependence of double-plasmon excitations in simple metals

Received 4 March 2008; published 29 May 2008Double plasmons are unique fingerprints of dynamical correlations in the model of a free-electron gasbeyond the random phase approximation. A combined experimental and theoretical study of double-plasmonexcitations in three simple metals Na, Mg, and Al is presented. The intensities, spectral shapes, and dispersionsof these excitations are analyzed as a function of momentum. The measured double-plasmon intensity is foundto increase with a decreasing electron density, which is in good agreement with the expectations of strength ofthe correlation effects as a function of the electron gas density. The overall quantitative agreement between theexperimental and the theoretical results is very good, while the remaining discrepancies may be due to higherorder correlation effects and band-structure effects.DOI: 10.1103/PhysRevB.77.195125 PACS number s : 78.70.Ck, 71.10.Ca, 71.45.Gm