Hole-pair symmetry and excitations in the strong-coupling extended t-Jz model: competition between d-wave and p-wave

Abstract

We analytically calculate the ground state pairing symmetry and excitation spectra of two holes doped into the half-filled t-t'-t"-Jz model in the strong-coupling limit (Jz>>|t|,|t'|,|t"|). In leading order, this reduces to the t'-t"-Jz model, where there are regions of d-wave, s-wave, and (degenerate) p-wave symmetry. We find that the t-Jz model maps in lowest order onto the t'-t"-Jz model on the boundary between d and p symmetry, with a flat lower band in the pair excitation spectrum. In higher order, d-wave symmetry is selected from the lower pair band. However, we observe that the addition of the appropriate t'<0 and/or t''>0, the signs of t' and t" found in the hole-doped cuprates, could drive the hole-pair symmetry to p-wave, implying the possibility of competition between p-wave and d-wave pair ground states. (An added t'>0 and/or t" <0 generally tend to promote d-wave symmetry.) We perturbatively construct an extended quasi-pair for the t-Jz model. In leading order, there are contributions from sites at a distance of sqrt{2} lattice spacings apart; however, contributions from sites 2 lattice spacings apart, also of the same order, vanish identically. Finally, we compare our approach with analytic calculations for a 2x2 plaquette and with existing numerical work, and discuss possible relevance to the physical parameter regime.