Attractive pairing potential from the repulsive extended Hubbard model on a two dimensional square lattice

The authors have examined the two dimensional repulsive extended Hubbard model on a square lattice, using standard many-body diagrammatic techniques. By summing an infinite series of two renormalised loops for the self-energy, they have found that for specific regions in the parameter space of (U,W), the renormalised Coulomb interaction can become attractive. In addition they have also included the effects of second order diagrams, pertaining to paramagnon effects in BCS superconductors. These results may form the basis for a mechanism of high Tc superconductors