SUPERCONDUCTING GAP NODAL SURFACE AND FERMI-SURFACE - THEIR PARTIAL OVERLAP IN CUPRATES

Electron correlation in cuprates leads to a global constraint Sigma(k) Delta(k) = 0 on the gap function Delta(k), resulting in a gap nodal s urface. We give numerical results and qualitative physical arguments s upported by some experimental results to argue that correlations also lead to a local constraint on charge fluctuations in k-space close to the Fermi surface, which may result in a substantial overlap of the Fe rmi surface with the gap nodal surface.