  We consider the repulsive Hubbard model on a square lattice with an
additional term, W, which depends upon the square of a single-particle
nearest-neighbor hopping. At half-band filling, constant W, we show that
enhancing U/t drives the system from a d-wave superconductor to an
antiferromagnetic Mott insulator. At zero temperature in the superconducting
phase, spin-spin correlations follow a powerlaw: exp(-i r Q) |r|^(-alpha). Here
Q = (pi, pi) and alpha is in the range 1 < alpha < 2 and depends upon the
coupling constants W and U. This results is reached on the basis of large scale
quantum Monte-Carlo simulations on lattices up to 24 times 24, and is shown to
be independent on the choice of the boundary conditions. We define a pairing
(magnetic) scale by the temperature below which short range d-wave pairing
correlations (antiferromagnetic fluctuations) start growing. With finite
temperature quantum Monte Carlo simulations, we demonstrate that both scales
are identical over a large energy range. Those results show the extreme
compatibility and close interplay of antiferromagnetic fluctuations and d-wave
superconductivity.

Strongly Correlated Electrons;Superconductivity