STUDY OF DISORDERED SYSTEMS

Abstract

The present thesis contains some of the author's theoretical investigations aimed at understanding the behaviour of electrons and phonons in disordered systems. The usual tools of band theory are not applicable to such systems because of the lack of translational invariance. With the breakdown of Bloch-Floquet theorem in disordercid systems) the nature and distribution of their eigen-states in energy become the foci of theoretical interest. With the availability of high-speed computers, it has become possible to apply sophisticated Green-function techniques to the present problem. Amorgst the analytical tools developed for studying disordered systems the Coherent potential approximation (CPA) occupies a central position. This theory has proved extremely helpful in providing a semi-quantitative description of a wide class of elementary excitations (electrons, phonons: excitons etc.).in disordered systems