A functional integral approach to the Anderson lattice with f-f hopping

The heavy-fermion systems are characterised by the coexistence of very strong local f level correlations with itinerant or band behaviour. In the periodic Anderson model (Anderson lattice), the localised f electrons can move only by hybridising with the conduction band. In the paper, the authors consider the effect of adding a direct f level hopping to the periodic Anderson model. They use a mean-field approximation to a function integral technique and impose the strong electron-electron correlation by using the slave boson approach. The authors show that, even for quite small values of the hopping, the properties of the model resemble those of a Hubbard model rather than a periodic Anderson model, with the specific heat being several times larger than for the Anderson lattice. Some consequences for real heavy-fermion systems are considered.