Static and dynamic susceptibility of a mixed-valence impurity

Abstract

A mixed-valence Anderson impurity with orbital degeneracy and the two active configurations corresponding to ${4f}^{0}$ and ${4f}^{1}$ is considered in the $U\ensuremath{\rightarrow}\ensuremath{\infty}$ limit. The static charge and spin susceptibilities are obtained through the one-$f$-electron propagators and compared with the results within the Brillouin-Wigner scheme. The dynamic susceptibilities are calculated by means of Mori's technique. The charge- and spin-relaxation rates are discussed, as well as bumps due to charge excitations.