Unified Theory of Phasons and Polaritons in Charge Density Wave Systems

Abstract

A unified approach to long wave-length phasons and phason-polaritons in semiconducting quasi one-dimensional charge density wave (CDW) systems is given. Using Keldysh kinetic theory in the quasi-classical approximation, expressions for linear CDW currents and CDW phase are derived microscopically taking into account both elastic and inelastic quasi-particle collisions. From these, a dielectric tensor for CDW is constructed which covers the full range of collision cases. The dielectric tensor is built from longitudinal and transverse conductivity functions and generalized condensate densities which are microscopically defined. They depend not only on wave number, frequency, and temperature but also on elastic and inelastic collision rates for quasi-particles. The dielectric tensor is combined with Maxwell's equations. This allows a systematical study of phason and phason-polariton spectra. Especially, the limits of collision dominated and collisionless quasi-particle gas are considered. A detailed comparison with earlier work is made. The continuity of the spectra at the wave-number origin is found to hold generally. Phasons in wires and films which can be investigated by microwave and optical probes are also studied.