QUASI-PARTICLES IN HEAVY-FERMION SYSTEMS WITH NEARLY INTEGER VALENCE

The theory describing the electron mass enhancement in Kondo-lattice h eavy-fermion systems is presented. The description is based on the pic ture of a spin Fermi liquid of RVB type which strongly interacts with conduction electrons. It is shown that the electron-spinon scattering results in large phase shifts for conduction electrons near the Fermi level which mimic the resonance renormalization but does not involve f -electron states. The results are compared with dHvA data for several Ce-based compounds.