Hole-pair symmetry and excitations in the strong-coupling extended t-Jz   model: competition between d-wave and p-wave
  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. 
R. M. Fye (1), G. B. Martins (2) and E. Dagotto (2) ((1) University of   New Mexico, Albuquerque, (2) NHMFL-Florida State Un...