Quasiparticles in heavy-fermion systems with nearly integer valence

The theory describing the electron mass enhancement in Kondo-lattice heavy-fermion systems is presented. The description is based on the picture 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.