Acoustic plasmons in two- and three-component degenerate Fermi gases, with application to the gallium arsenide electron-hole plasma

Abstract

Acoustic plasmons in a two-component degenerate Fermi gas are analysed, using the random-phase approximation dielectric function with exact analytic continuation into the lower half of the complex frequency plane. The acoustic plasmon spectrum, in reduced variables, depends on four parameters-the ratio of Thomas-Fermi screening wavevectors of the two plasmas, the ratio of Fermi velocities, and the densities of the two plasmas. The dependence of the spectrum on these parameters is surveyed. The first two of the above-mentioned parameters are the most important. Acoustic plasmons can exist even when the two plasmas have equal effective mass. The range of parameters giving weakly damped acoustic plasmons is described. The spectrum has an abrupt cut-off (maximum wavevector); this corresponds to the onset of Landau damping in both plasmas. The experimental results of Pinczuk, Shah and Wolff (1981) on acoustic plasmons in the GaAs electron-hole plasma are reanalysed. For this purpose the extension to a three-component plasma is made, since the light holes, although few in number, have a significant effect on the results. In this system the 'upper acoustic plasmon' does not exist, contrary to what is implicitly assumed by Pinczuk, Shah and Wolff in their analysis. The 'lower acoustic plasmon' does exist, and its phase velocity agrees, within the errors of theory and experiment, with their experimental result.