Cooper pairing between conduction and localized electrons in heavy-fermion systems

We study the Cooper pairing between a conduction electron (c electron) and a localized f electron in heavy-fermion systems. Applying the Schrieffer-Wolff transformation to the periodic Anderson model, we obtain an effective Hamiltonian for describing the c-f pairing superconductivity. The effective Hamiltonian includes direct and spin-exchange interactions between c and f electrons, which can be the driving force for the formation of Cooper pairs. Within the mean-field approximation, we show that the c-f pairing state with anisotropic s-wave symmetry is stabilized in a wide range of parameters.