Dx2-y2 superconductivity in a model of correlated fermions.

Abstract

A two-dimensional fermionic model with attractive interactions is discussed. Its form is motivated by the phenomenology of the underdoped high-{ital T}{sub {ital c}} cuprates, as discussed in previous literature. The exact solution to the two-particle problem leads to a bound state in the {ital d}{sub {ital x}{sup 2}{minus}{ital y}{sup 2}} subspace. Numerical techniques show that the model has strong {ital d}{sub {ital x}{sup 2}{minus}{ital y}{sup 2}} pairing correlations in the ground state at low fermionic density. Within a self-consistent random phase approximation diagrammatic study, the model has a {ital d}-wave superconducting (SC) phase. The density dependence of the critical temperature is calculated. We argue that in the context of {ital d}-wave SC this model fulfills the role that the attractive on-site Hubbard model has played for {ital s}-wave SC. We also show that another candidate, the attractive {ital t}-{ital U}-{ital V} model, is actually not useful as a toy model for {ital d}-wave SC for a variety of reasons. {copyright} {ital 1996 The American Physical Society.}