Classification of the interlayer coupling in high-Tccuprates from low-field magnetization studies

Low-field magnetization M(H) measurements are reported for single crystals of various high-${\mathit{T}}_{\mathit{c}}$ cuprates with different anisotropies (γ=${\lambda }_{\mathit{c}}$/${\lambda }_{\mathit{ab}}$, where ${\lambda }_{\mathit{c}}$ and ${\lambda }_{\mathit{ab}}$ are the c-axis and ab-plane penetration depths). For ${\mathrm{YBa}}_2$ ${\mathrm{Cu}}_3$ ${\mathrm{O}}_7$ (γ≊5) and ${\mathrm{La}}_{1.89}$ ${\mathrm{Sr}}_{0.11}$ ${\mathrm{CuO}}_4$ (γ≊12), qualitatively similar M(H) behavior is observed when the magnetic field is applied both perpendicular (H∥c) and parallel (H∥ab) to the ${\mathrm{CuO}}_2$ planes, consistent with a description of these compounds as anisotropic three-dimensional superconductors. ${\mathrm{Tl}}_2$ ${\mathrm{Ba}}_2$ ${\mathrm{CuO}}_{6+\mathrm{\delta }}$ (γ≊25) and ${\mathrm{Bi}}_2$ ${\mathrm{Sr}}_2$ ${\mathrm{CaCu}}_2$O (γ≊250), on the other hand, show significant differences in M(H) with H∥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 ${\xi }_{\mathit{c}}$ to the interlayer spacing s. © 1996 The American Physical Society.