Systematic study of d-wave superconductivity in the 2D repulsive Hubbard   model
  The cluster size dependence of superconductivity in the conventional two-dimensional Hubbard model, commonly believed to describe high-temperature superconductors, is systematically studied using the Dynamical Cluster Approximation and Quantum Monte Carlo simulations as cluster solver. Due to the non-locality of the d-wave superconducting order parameter, the results on small clusters show large size and geometry effects. In large enough clusters, the results are independent of the cluster size and display a finite temperature instability to d-wave superconductivity. 
T.A. Maier, M. Jarrell, T.C. Schulthess, P.R.C. Kent, J.B. White