Investigations of the interlayer coupling in high-T-c cuprates

Low-field magnetization M(H) measurements can be used to probe the nature of the screening currents and the interlayer coupling in high-T-c cuprates. Here we compare the M(H) behaviour of single crystals of Bi2Sr2CaCu2O8 and fully oxygenated and oxygen reduced YBa2Cu3O7-delta. In YBa2Cu3O7, the M(H) behaviour is consistent with anisotropic 3D superconductivity whilst in Bi2Sr2CaCu2O8, the surface screening currents are strongly affected by the presence of vortices, implying that the CuO2 planes are coupled via a weak Josephson interaction. In oxygen-deficient YBa2Cu3O6.7 (T-c = 63K), the M(H) behaviour at low temperatures is similar to that found for Bi2Sr2CaCu2O8, implying that the removal of oxygen from the chains has resulted in a dimensional crossover of the superconducting state in YBa2Cu3O7-delta. As the temperature approaches T-c, the 3D behaviour is eventually restored as the c-axis coherence length xi(c) becomes comparable with the interlayer spacing d.