Dimensional cross-over in the superconducting state of oxygen-deficient YBa 2Cu 3O 6.7

Abstract

We have investigated the dimensionality of the superconducting state in oxygen reduced YBa 2Cu 3O 6.7 ( T c = 63 K_via measurements of the low-field magnetization M( H) with the field applied parallel to the CuO 2-planes. At low temperatures, the c-axis surface screening currents are found to be strongly suppressed by vortices penetrating between the planes, indicating that the individual CuO 2-planes are weakly coupled via the Josephson interaction. Since in optimally doped YBa 2Cu 3O 7, the M( H) behaviour is consistent with anisotropic three-dimensional superconductivity, these observations clearly demonstrate that the removal of oxygen from the chains results in a dimensional cross-over of the superconducting state in YBa 2Cu 3O 7−δ. On raising the temperature towards T c, three-dimensional behaviour is again observed in YBa 2Cu 3O 6.7 when the c-axis coherence length becomes comparable to the interlayer spacing.