Critical temperature for the two-dimensional attractive Hubbard model

The critical temperature for the attractive Hubbard model on a square lattice is determined from the analysis of two independent quantities, the helicity modulus ρ_s and the pairing correlation function P_s. These quantities have been calculated through quantum Monte Carlo simulations for lattices up to 18×18, and for several densities, in the intermediate-coupling regime. Imposing the universal-jump condition for an accurately calculated ρ_s, together with thorough finite-size scaling analyses (in the spirit of the phenomenological renormalization group) of P_s, suggests that T_c is considerably higher than hitherto assumed.