ON THE ORIGIN OF d-WAVE PAIR FUNCTIONS IN HIGH-Tc SUPERCONDUCTIVITY

Abstract

We argue that the usual Hubbard's model produces only s-wave pairing functions and, even then, only at unphysically large values of the lumped parameter J≡4t2/U. It follows that a reliable theory of high-Tc superconductivity has to include additional features if it is to reproduce the d-wave gap. We test the effects of an alternating potential caused by a charge stripe, on the ground state of the Hubbard model in strong-coupling. If we "fine tune" we do find the d-waves. However, a better-formulated version of a three-band model yields a sturdier theory of pair formation in high-Tc superconductivity. The coupling constant g1=t2/V factors out, hence it serves only to establish the unit of energy; the underlying Hamiltonian is universal. We outline the principal properties of this model, including the intimate relation between charge-density stripes and the d-wave pair function, its rejection of 45° stripes (checkerboard pattern), and other concerns.