Electronic Theory for Bilayer-Effects in High-T_c Superconductors

The normal and the superconducting state of two coupled CuO_2 layers in the High-T_c superconductors are investigated by using the bilayer Hubbard model, the FLEX approximation on the real frequency axis and the Eliashberg theory. We find that the planes are antiferromagnetically correlated which leads to a strongly enhanced shadow band formation. Furthermore, the inter-layer hopping is renormalized which causes a blocking of the quasi particle inter-plane transfer for low doping concentrations. Finally, the superconducting order parameter is found to have a d_{x^2-y^2} symmetry with significant additional inter-layer contributions.