Optical phonon spectrum rearrangement in quasi-one-dimensional disordered systems

Abstract

By employing the Green's-function expansion method, the optical spectrum rearrangement in the quasi-one-dimensional (1D) impurity vibrational systems has been investigated. Based on the validity criteria for the conventional coherent potential approximation (CPA), the dispersion of phononlike modes and main parameters for the rearranged spectra are determined. The most interesting rearrangement occurs when the bandwidth exceeds the limiting frequency of the optical branch. In this case, the spectrum rearrangement exhibits features characteristic of both the acoustic branch and high-frequency optical branch. Formations of the impurity optical branch and a well-defined limiting frequency are described. [S0163-1829(99)00626-8]