Superconductivity in the Kondo lattice

Superconductivity in the Kondo lattice was theoretically studied in connection with superconductivity in CeCu₂{Si}₂$ and U${Be}₁₃$. To achieve superconductivity in these systems, coherence between Ce ions or U ions is of crucial importance. To take account of the coherence, the periodic Anderson model with a small dispersion of the f band was used. With the use of a single-site approximation for the self-energy of the f electron, the heavy fermion state near the Fermi level was derived. This state is a highly correlated state, and the Coulomb repulsive interaction is strongly reduced. The f electrons are found to be responsible for superconductivity. Both the specific heat in the normal state CN(T) and the specific-heat jump ΔC at Tc are very large, and the ratio ΔCCN(Tc) has the BCS value in the weak-coupling approximation. The thermodynamic critical field is very high.