PUB - Publikationen an der Universität Bielefeld

The general equations determining the quasiparticle, spin, and charge excitations of two coupled Hubbard planes are derived within the inverted perpendicular matrix or fluctuation-exchange approximation, For equal intralayer and interlayer Coulomb repulsions we obtain s(+/-) wave superconducting gaps with opposite signs in the two bands, The magnitude of this gap is highly anisotropic but is far away from exhibiting a zero. The resulting spin susceptibility develops a spin gap and a commensurate peak at higher frequency as T decreases below T-c. This is quite similar to the results for the d(x2-y2) wave gap and agrees qualitatively with neutron scattering on YBa2Cu3O7 below T-c.