D-WAVE SUPERCONDUCTIVITY IN THE T-J MODEL USING A SYSTEMATICALLY IMPROVED VARIATIONAL MONTE-CARLO METHOD

We can construct unbiased systematic improvements of standard Variational Monte Carlo calculations by the use of wavefunctions modified by short range operators. Using the energy and spectral width of the original and improved wavefunctions we can judge the quality fo the trial wavefunctions. For the t-J model we find the regions of phase separation and d-wave superconductivity with varying J/t and hole density delta and extend the T = 0 phase diagram into the physically interesting region of delta similar to 0.1-0.2 and J/t similar to 0.4. Above the critical ratio of J/t/(c) we find clear evidence of d(x2-y2)-pairing and above a higher value J/t/(s) phase separation. At delta = 0.16 we obtain values J/t/(c) = 0.4 and J/t/(s) = 0.7. Cluster sizes up to 50 sites are used.