Classification of the interlayer coupling in high-T-c cuprates from low-field magnetization studies

Low-field magnetization M(H) measurements are reported for single crystals of various high-T-c cuprates with different anisotropies (gamma = lambda(c)/lambda(ab), where lambda(c) and lambda(ab) are the c-axis and ab-plane penetration depths). For YBa2Cu3O7 (gamma approximate to 5) and La1.89Sr0.11CuO4 (gamma approximate to 12), qualitatively similar M(H) behavior is observed when the magnetic field is applied both perpendicular (H parallel to c) and parallel (H parallel to ab) to the CuO2 planes, consistent with a description of these compounds as anisotropic three-dimensional superconductors. Tl2Ba2CuO6+delta (gamma approximate to 25) and Bi2Sr2CaCu2O (gamma approximate to 250), on the other hand, show significant differences in M(H) with H parallel to ab which can be attributed to the presence of Josephson screening currents across the layers. These observations imply that the nature of the interlayer coupling is determined primarily by the ratio of the out-of-plane coherence length xi(c) to the interlayer spacing s