Interaction of optical and acoustic phonons with longitudinal plasma waves

Abstract

In this paper the interaction between the longitudinal plasma wave and the lattice waves is examined by a self-consistent field approach. The propagation characteristic of a longitudinal plasma wave under the influence of an applied longitudinal electric field is examined by means of the Boltzmann transport equation. The solutions for the lattice waves are derived by using a linear chain model. This approach leads to a combined dispersion relation consisting of three branches representing respectively, electron plasma, optical phonons and acoustic phonons; and give a clear exposition of the interaction between the collective electron modes and the lattice modes. The combined dispersion relation reduces essentially to the acoustical and optical cases where some special cases have been obtained previously. Due to the strong interaction between the optical phonons and plasma waves, the optical reststrahlen frequency is raised while the plasma frequency is lowered. The acoustic phonons can have gain under application of a suitable drift field. The form of the attenuation constant suggests that the optical phonons can also have gain; however, our theory cannot apply due to the large drift field required.