Finite size effect in Bi2Sr2CaCu2O(8+d) and YBa2Cu3O6.7 probed by the in-plane and out of plane penetration depths

Abstract

We report on a systematic finite size scaling analysis of in-plane penetration depth data taken on Bi$_{2}$Sr$_{2}$CaCu$_{2}$O$_{8+\delta}$ epitaxially-grown films and single crystals, and of in-plane and out of plane data taken on YBa$_{2}$Cu$_{3}$O$_{6.7}$ aligned powder. It is shown that the tails in temperature dependence of the penetration depths, appearing around the transition temperature, are fully consistent with a finite size effect. This uncovers the granular nature of these cuprates, consisting of superconducting homogeneous domains of nanoscale extent, embedded in a non-superconducting matrix.