An Extension of the Coherent-Potential Approximation. II: Single-Particle Excitation Functions

Abstract

On the basis of an extension of the coherent-potential approximation, the single-particle excitation function of a quasi-particle in a substitutionally disordered system is formulated for the Hamiltonian with off-diagonal disorder in addition to diagonal one. A particular attention is paid to the effect of site-dependence of the strength of coupling between a quasi-particle and an external quantum. The formalism is applicable to the case where the inverse of the propagator of the quasi-particle is a quasi-additive random operator. The theory is compared with other existing theories which have their own ranges of applicability.