Superconducting Condensation Energy of the Two-Dimensional Hubbard Model in the Large-Negative-t′ Region

We compute the superconducting condensation energies E-cond of Hg1201 and Tl2201 cuprates by applying the variational Monte Carlo method to the two-dimensional Hubbard model, first, with the specific band parameters t' = 2t '' = -0.25t appropriate for these highest-T-c single-CuO2-layer cuprates; t, t', and t '' are the first-, second-and third-neighbor transfer energies, respectively. In the range of on-site Coulomb energy U of (7-10)t with optimal doping, we succeed in obtaining the bulk-limit E-cond values by extrapolating the results. They sharply increase with increasing U and become comparable to experimental values when U approximate to 9t. Next, E-cond values at t' = -2t '' = -0.18t demonstrate that with a fixed U the bulk-limit E-cond quickly increases with a decrease in vertical bar t'vertical bar = 2t '' in the large-vertical bar t'vertical bar region. Finally, we argue that the remoteness of the apex oxygen from the planar Cu in the two cuprates is considered to increase U and bring about the experimental magnitude of E-cond. The present scheme explains the observed correlation between T-c and t' among cuprates.