Effects of Interlayer Interaction on the Superconducting State in YBCO
  For a two layer system in a weak coupling BCS formalism any interlayer interaction, regardless of its sign, enhances the critical temperature. The sign has an effect upon the relative phase of the order parameter in each of the two planes but not upon its magnitude. When one of the planes has a dispersion consistent with CuO chains and no intrinsic pairing interaction there is both an enhancement of the critical temperature and an s+d mixing in both layers as the interlayer interaction is increased. The magnetic penetration depth, c-axis Josephson tunneling, density of states and Knight shift are calculated for several sets of model parameters. 
C. O'Donovan and J.P. Carbotte (McMaster University)