Superconducting Condensation Energy of the Two-Dimensional Hubbard Model in the Large-Negative-t' Region
We compute the superconducting condensation energies Econd 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-Tc 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\sim10)t with optimal doping, we succeed in obtaining the bulk-limit Econd values by extrapolating the results. They sharply increase with increasing U and become comparable to experimental values when U \approx 9t. Next, Econd values at t' = -2t" = -0.18t demonstrate that with a fixed U the bulk-limit Econd quickly increases with a decrease in |t'| = 2t" in the large-|t'| 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 Econd. The present scheme explains the observed correlation between Tc and t' among cuprates.