Kosterlitz-Thouless transition in two-dimensional hubbard model evidenced from quantum Monte Carlo calculations of susceptibilities

Susceptibilities in the static limit ω → 0 are evaluated to show that the superconducting Kosterlitz-Thouless transition exists in the two-dimensional Hubbard model for optimal band parameters. By using quantum Monte Carlo methods, we have examined the size dependence of the spin susceptibility χ(Q) at half filling and the pair susceptibilities with d- and s-wave symmetries for the repulsive and attractive interactions, respectively. The numerical results for systems of up to 14x14 sites show that the s-wave pair susceptibility scales as χpair - L2 for the attractive case, in agreement with previous quantum Monte Carlo studies. The scaling χpair - L2 also holds for the d-wave pair susceptibility for the repulsive Hubbard model if we adjust the band parameter t'. Therefore, it is likely that the superconducting Kosterlitz-Thouless transition exists in the two-dimensional repulsive Hubbard model. (author)