COOPER PAIRING NEAR THE BOUNDARY IN THE -U HUBBARD-MODEL

The Cooper pairing near the boundary of a superconductor is analyzed b y using the linear-response theory. The system is described by the squ are lattice (t, -U) Hubbard model occupying halfspace. At half filling , the pairing also corresponds to the antiferromagnetic ordering in th e repulsive Hubbard model. The numerical result clearly shows that, at weak to intermediate coupling (U/t less than or equal to 1), the boun dary exerts strong influence on the order parameter; the weaker the co upling, the deeper the order parameter is suppressed near the boundary . The present scheme is valid in the whole temperature regime of Coope r pairing.