Parameter dependence of the superconducting condensation energy of the two-dimensional Hubbard model

Using the variational Monte Carlo method we have computed the t'-dependence of the superconducting condensation energy for the titled model of the size up to 20x20 with electron densities congruent with 0.86 and 0.84. The energy starts to sharply rise when t' decreases from 0 to -0.10, reaching the maximum around -0.05 to -0.10 and turns to slow decrease, vanishing around -0.35 (in energy unit t). The rising part is in a qualitative agreement with observations