Effects of crystalline-electric-field on valence fluctuations in an extended Anderson model

Abstract

We investigate a two-orbital impurity Anderson model (where two orbitals correspond to the two crystalline-electric-field (CEF) doublets) with Coulomb repulsions U fc between the f- and conduction electrons. Using the Wilson numerical renormalization group method, we calculate the f-electron valence susceptibility. As the U fc increases, the character of dominant valence fluctuation changes from off-diagonal ( f † c + c † f ) to diagonal ( f † f - c † c ) one, where f † and c † stands for the creation operator of f- and conduction electrons, respectively. In the valence-fluctuation regime, we find that the CEF splitting is smeared out and the effective degeneracy becomes 4-fold, leading to the strong valence fluctuations.