Finite-size effect in Bi2Sr2CaCu2O8+δ and YBa2Cu3O6.7 probed by the in-plane and out-of-plane penetration depths -: art. no. 024502

We report on a systematic finite-size scaling analysis of in-plane penetration depth data taken on Bi2Sr2CaCu2O8+delta epitaxially grown films and single crystals, and of in-plane and out-of-plane data taken on YBa2Cu3O6.7 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 nonsuperconducting matrix.