Plasmon Sidebands in Alkali Metals

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Abstract
Recent experiments suggest the presence of plasmon sidebands in interband absorption spectra of the simple metals. A previous calculation of the sideband intensity considered plasmon emission in the final state, including interference corrections (charge cancellation of electron and hole). These reduce the plasmon intensity about 60%. Here previous work is extended in several directions: (1) allowance is made for plasmon effects in the initial state; (2) recoil and dispersion effects are included; and (3) the dependence of sideband intensity on initial electron momentum is explicitly considered. In this improved model charge cancellation reduces the sideband intensity by more than an order of magnitude. This reduction was first noticed by Brouers for the analogous case of soft-x-ray emission in simple metals. Plasmonemission structure is almost two orders of magnitude weaker than interband absorption for Na, K, Rb, and Cs in the model considered here. These results are inconsistent with recent interpretations of pronounced satellite structure in the optical data of simple metals.