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. 
Kunihiko Yamaji, Takashi Yanagisawa, Mitake Miyazaki, and Ryosuke   Kadono
cond-mat.supr-con