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 crys tals of various high-T-c cuprates with different anisotropies (gamma = lambda(c)/lambda(ab), where lambda(c) and lambda(ab) are the c-axis a nd ab-plane penetration depths). For YBa2Cu3O7 (gamma approximate to 5 ) and La1.89Sr0.11CuO4 (gamma approximate to 12), qualitatively simila r M(H) behavior is observed when the magnetic field is applied both pe rpendicular (H parallel to c) and parallel (H parallel to ab) to the C uO2 planes, consistent with a description of these compounds as anisot ropic three-dimensional superconductors. Tl2Ba2CuO6+delta (gamma appro ximate to 25) and Bi2Sr2CaCu2O (gamma approximate to 250), on the othe r hand, show significant differences in M(H) with H parallel to ab whi ch can be attributed to the presence of Josephson screening currents a cross the layers. These observations imply that the nature of the inte rlayer coupling is determined primarily by the ratio of the out-of-pla ne coherence length xi(c) to the interlayer spacing s.