Density of states for elementary excitations in the Kondo problem

Abstract

The density of states for the elementary excitations in the Kondo problem is investigated with the use of the exact solution for the impurity models. Two kinds of dressed particles, representing the charge and spin excitations, respectively, are introduced for the Anderson model. Excitation spectra for these particles clearly describe the formation of the narrow Kondo resonance and the deep-lying charge-excitation hump. It is shown that all kinds of elementary excitations can be described in terms of these dressed particles. Then the calculation is extended to the orbitally degenerate case. The maximum structure appearing in the density of states for the rare-earth impurity system is discussed with the use of the highly correlated degenerate Anderson model. The multichannel Kondo model is investigated to discuss the excitations in the orbital singlet case as for the transition-metal impurity, and also to discuss the nontrivial screening effect introduced by Nozi\`eres and Blandin.