Optical Properties of Metals: Many-Electron Effects

Abstract

The work reported here, which deals with the influence of electron-electron interactions on the optical properties of metals, is motivated by existing discrepancies between the observed interband absorption and that calculated within the random-phase approximation (RPA). These interactions are treated systematically using a self-consistent conserving-approximation scheme. Both vertex and quasiparticle renormalization effects transcending the RPA are considered on an equal footing. Repeated first-order scattering of a quasielectron and a quasihole via the dynamically screened Coulomb interaction is the principal process investigated. The contributions are of two kinds: one associated with a statically screened Coulomb interaction and the other with exchange of virtual plasmons. The latter contribution, although larger than the former, is substantially cancelled, to within about 10% in Al, by quasiparticle dressing effects due to virtual plasmons. Those second-order effects in the dynamically screened interactions, whose inclusion guarantees a conserving approximation, are also negligible. Recent experimental data for Al are reviewed and new theoretical calculations within the RPA presented which appreciably reduce the existing discrepancies. These provide support for the present conclusion that electron-electron interactions do not significantly affect the optical absorption. Previous calculations for Na are discussed and the situation there may well be similar.