Odd-parity singlet pairing in the positive-U Hubbard model

We consider the possibility of an odd-parity singlet pairing in the positive-U Hubbard model, which naturally incorporates short-ranged antiferromagnetic correlations in the ground state. In a quantum Monte Carlo simulation of a nearly half-filled Hubbard model, we find that the repulsive U enhances the tendency for this type of pairing more strongly than for other pairing channels considered earlier. We propose a BCS-type wave function for this pairing where the gap has no nodes over the Fermi surface, and discuss various experimental consequences in connection to high-Tc superconductivity