A general approach to charge/spin density waves electrodynamics

(Received 26 February 1993, revised 13 August 1993, accepted 17 August 1993)

Abstract
We reconsider microscopic grounds for the electric field response and for the phase dynamics of charge/spin density waves in pure systems. We suggest transparent and free of lengthy calculations way to derive the local Lagrangian valid at any temperature and for arbitrary electronic spectrum provided it supports the existence of the long range DW order below the mean field transition temperature . The analysis is based on classification of normal carriers in two categories - intrinsic and extrinsic ones with respect to the DW gap vicinity, and on a proper treatment of perturbative and nonperturbative (the so-called anomalies) contributions. This approach results e.g. in a helpful relation between the "generalized condensate density" and the complex dielectric susceptibility of intrinsic carriers. On this basis we easily describe main properties of the DW's both at low T and near . Separately for CDW and SDW we discuss the spectra and the attenuation for the TO and LO modes, the low frequency relaxation and the reaction to an external voltage. Our studies cover systematically and generalize most of the previously derived results which have been used for pure systems or as preliminary steps to approaching the pinning problem. New results of a potential experimental significance describe the TO, LO and zero sound spectra interplay, the anomalous Landau damping of both LO and TO modes near , the relaxation rates for narrow gap DW's, the relation between the current and the driving electric field and between the inherent and the observed nonlinear conductivity.