Theory of a uranium impurity in metals fluctuating between two magnetic configurations

The theory of a uranium impurity in a metal fluctuating between two magnetic valence states is presented. The ground and a few excited states of the uranium ion are examined with orbital degeneracy embedded in a free electron matrix fluctuating between f2 and f3 states. For the minimum allowed orbital degeneracy variational states of different spin multiplicity are constructed, namely singlet, doublet, triplet and quartet, and their binding energies relative to the Fermi sea are calculated. It is shown how the same results may be obtained in the large N(=2j+1) limit of the same model written in the j-j coupling scheme (for zero j.j coupling). It is found that in the intermediate valence regime and in both Kondo regimes, the ground state is a singlet, in agreement with recent experiments on dilute alloys, Usub(x)Ysub(1-x)Sb. (author)