Is a well-defined resonance mode always a precursor for a cross-type spectrum rearrangement?

Abstract

Using the model of a one-dimensional disordered system, we have demonstrated that a spectrum rearrangement of the normal cross type does not always take place under an increase in the impurity concentration when a single impurity center yields a well-defined resonance mode. This unusual behavior is attributed to weak scattering near the resonance frequency for the chosen type of impurity center. As opposed to the ordinary case, an impurity must be strongly bound to produce a resonance mode, and the subsequent spectrum rearrangement appears to be of the anomalous type. Spectrum rearrangement is investigated based on a series expansion of the one-particle Green's function in terms of groups of interacting impurity centers.