Kondo effect in Fermi systems with a gap: A renormalization-group study

Abstract

We present the results of a Wilson renormalization-group study of the single-impurity Kondo and Anderson models in a system with a gap in the conduction-electron spectrum. The behavior of the impurity susceptibility and the zero-frequency response function, T«Sz;Sz» are discussed in the cases with and without particle-hole symmetry. For the case of no particle-hole symmetry, we find a transition, as the bandgap Δ increases, from a singlet ground state (when Δ≪TK, where TK is the Kondo temperature) to a doublet ground state (when Δ ≫TK). But there is no such transition for the case with particle-hole symmetry: the ground state is always a doublet. In addition, for the asymmetric Anderson model the correlation functions, 〈S + (combining right arrow above)·σ + (combining right arrow above)(0)〉, 〈nd〉, and 〈nd(2-nd)〉 are computed.