U−Jsynergy effect for high-Tcsuperconductors

Abstract

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 ${d}_{{x}^{2}\ensuremath{-}{y}^{2}}$ 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 ${d}_{{x}^{2}\ensuremath{-}{y}^{2}}$ superconducting and antiferromagnetic correlations.