U-J synergy effect for high-Tc superconductors -: art. no. 064519

Using the renormalization group with included self-energy effects and exact diagonalization of small clusters we investigate the ground-state phase diagram of a two-dimensional extended Hubbard model with nearest-neighbor exchange interaction J, in addition to the local Coulomb repulsion U. The main instabilities are antiferromagnetism close to half filling and d(x)2(-y)2 superconductivity in the doped system. We find that self-energy effects are fatal for superconductivity in the repulsive Hubbard model (i.e., J=0, U>0). The superconductivity is triggered by finite J. The combined action of J and U interactions provide a remarkably efficient, mechanism to enhance both d(x)2(-y)2 superconducting and antiferromagnetic correlations.