Mass enhancement in an intermediate-valent regime of heavy-fermion systems

Kubo, Katsunori 

We study the mechanism of the mass enhancement in an intermediate valent regime of heavy fermion materials. We find that the crossovers between the Kondo, intermediate valent, and almost empty -electron regimes become sharp by the Coulomb interaction between the conduction and electrons. In the intermediate valent regime, we find a substantial mass enhancement, which is not expected in previous theories. Our theory may be relevant to the observed non-monotonic variation of the effective mass under pressure in CeCuSi and the mass enhancement in intermediate valent compounds - and -YbAlB.