Quantum Monte Carlo Evidence for d-wave Pairing in the 2D Hubbard Model at a van Hove Singularity

We implement a Quantum Monte Carlo calculation for a repulsive Hubbard model with nearest and next-nearest neighbor hopping interactions on clusters up to 12x12. A parameter region where the Fermi level lies close to the van Hove singularity at the Saddle Points in the bulk band structure is investigated. A pairing tendency in the $d_{x^2-y^2}$ symmetry channel, but no other channel, is found. Estimates of the effective pairing interaction show that it is close to the value required for a 40 K superconductor. Finite-size scaling compares with the attractive Hubbard model.