Ch. Pao et Ne. Bickers, ANISOTROPIC SUPERCONDUCTIVITY IN THE 2D HUBBARD-MODEL - GAP FUNCTION AND INTERACTION WEIGHT, Physical review letters, 72(12), 1994, pp. 1870-1873
A potential d(x2-y2) pairing state in the 2D Hubbard model is investig
ated within a conserving extension of Hartree-Fock theory known as the
fluctuation exchange approximation. The self-consistent field equatio
ns are solved with the aid of a recently developed renormalization gro
up approach for general models which lack a Migdal theorem. The calcul
ations yield an anisotropic gap which saturates rapidly below T(c) to
a peak value of 2DELTA(k)/kT(c) approximately 10-12 for k along the k(
x) and k(y) axes.