Detection of pairing correlation in the two-dimensional Hubbard model

The quantum Monte Carlo method is used to reexamine superconductivity in the single-band Hubbard model in two dimensions. Instead of the conventional pairing, we consider a ``correlated pairing,'' 〈c-${\mathrm{tilde}}_{\mathrm{i}\mathrm{\uparrow }}$c-${\mathrm{tilde}}_{{\mathrm{i}}^{|\mathrm{I}\mathrm{H}}\mathrm{\downarrow }}$〉 with c-${\mathrm{tilde}}_{\mathrm{i}\mathrm{\sigma }}$≡${\mathrm{c}}_{\mathrm{i}\mathrm{\sigma }}$(1-${\mathrm{n}}_{\mathrm{i}\mathrm{-}\mathrm{\sigma }}$), which is inferred from the t-J model, the strong-coupling limit of the Hubbard model. The pairing in the d-wave channel is found to possess both a divergence like 1/T in the pairing susceptibility and a growth of the ground-state pairing correlation with sample size, indicating an off-diagonal long-range order near (but not exactly at) half-filling.