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

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.