ANTIFERROMAGNETISM VERSUS SUPERCONDUCTIVITY IN A TIGHT-BINDING MODEL WITH SINGLET NEAREST-NEIGHBOR PAIRING INTERACTION

We study a tight-binding model with a singlet nearest-neighbor pairing interaction on a two-dimensional square lattice. In the strong coupli ng regime it undergoes an Ising-Like antiferromagnetic phase transitio n for all fillings. For this reason we include both an antiferromagnet ic and a superconducting order parameter within the symmetry-broken Ha rtree-Fock approximation and derive the phasediagram. In the half-fill ed state, the system orders antiferromagnetically; otherwise supercond uctivity occurs and might coexist with antiferromagnetism. The implica tions on the specific heat and Pauli susceptibility are discussed.