The effect of polarisation fluctuations on the optical response function

Abstract

A method is proposed for the estimation of the optical electron response function in a polar medium without recourse to perturbation theory. It has proved possible to write the temperature Green function of the electron coupled with a short-range potential and interacting (in a dipole approximation) with long-wave polarisation fluctuations proceeding from the functional integral representation. Using the steepest descent method in the high-temperature limit, comparatively simple expressions have been obtained. These are compared with experimental data for impurity ions in polar media and temperature dependences of the edge of the medium absorption band (Urbach rule).