Symmetry of the superconducting order parameter in the Anderson lattice model with nearest-neighbor attractive interaction

We study an extended version of the Anderson lattice model including a density-density attractive interaction between correlated electrons on nearest-neighbor sites. Using a perturbative expansion around the atomic limit for the normal phase and the broken-symmetry Hartree-Fock scheme for the attractive potential, we examine which of the possible symmetries of the superconducting order parameter leads to the highest transition temperatures, in the case of nearest-neighbor hopping on a square lattice. We find that in a wide range of electron densities around the half filling, the increase of the on-site Coulomb f-repulsion U changes the pairing symmetry from d-wave into p- or into anisotropic s-wave, depending on the parameter regime. For large values of U compared to the bandwidth, the superconducting phase is suppressed, regardless of the symmetry of the order parameter. The effects introduced by variations in the hybridization coupling are also analyzed.