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We show that the resonating-valence-bond mechanism for high-T₂ superconductivity can lead to s-wave- and d-wave-like superconducting order parameters. The critical temperature for d-wave ordering is higher close to half-filling. At low temperatures, a mixture of d and s waves with a well-defined phase opens a full gap in the quasiparticle spectrum.
Gabriel Kotliar (Tue,) studied this question.