Virtual bound states and f bands in mixed-valent systems

Experimentally observed properties of mixed-valent intermetallics are summarized. A model involving noninteracting fermions occupying (2J + 1)-fold degenerate resonance states is found very successful in reproducing the salient features of the experimental results. It is suggested that the key to this success lies in the existence of fermion-like quasi-particles occupying f-resonance states, whose motion is correlated in such a way that energetically unfavorable configurations of the f shell do not occur. (orig.)