Heavy fermions in the Kondo lattice as neutral quasiparticles and dHvA effect

The origin of heavy fermions in f-electron compounds with nearly integer valence is discussed. General arguments in favor of uncharged Fermi excitations of spin origin as the quasiparticles giving the main contribution to the low-T thermodynamics are present. We find a strong renormalization of the conduction band energy spectrum due to inelastic scattering by the spin-liquid which, however, is non-universal, and in the general case the effective mass of the charged carriers is less than the low-T thermodynamic mass. We show that the interaction with the spin liquid, in contrast with phonons, leads to the explicit Dingle factor in the amplitude of the dHvA effect.