Superconducting Condensation Energy of the Two-Dimensional Hubbard Model in the Large-Negative-t' Region

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We compute the superconducting condensation energies E_{\text{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_{\text{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_{\text{cond}} values by extrapolating the results. They sharply increase with increasing U and become comparable to experimental values when U \approx 9t. Next, E_{\text{cond}} values at t' = -2t''= -0.18t demonstrate that with a fixed U the bulk-limit E_{\text{cond}} 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 E_{\text{cond}}. The present scheme explains the observed correlation between T_{\text{c}} and t' among cuprates.
2011-08-15