ELECTRONIC THEORY FOR BILAYER EFFECTS IN HIGH-TC SUPERCONDUCTORS

Abstract The normal and the superconducting state of two coupled CuO2 layers in the high-Tc superconductors are investigated by using the bilayer Hubbard model, the fluctuation exchange approximation and the Eliashberg theory. We find that the planes are antiferromagnetically correlated. The inter-layer hopping is renormalized which causes a blocking of the quasi-particle inter-plane transfer. This is related to the fact that each inter-layer hopping process is accompanied by spin-flips due to the opposite antiferromagnetic environment in the other plane. Thus, due to the corresponding large inter-plane scattering rates, an incoherent coupling of the layers occur. Finally, the superconducting order parameter is found to have a dx2-y2 symmetry, where the d-wave state is characterized by a large contribution of inter-layer pairing such that Cooper pairs are formed by electrons from the same layer as from different layers with almost equal probability.