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

TL;DR

This study analyzes the finite size effects in the penetration depths of cuprate superconductors, revealing their granular structure with nanoscale superconducting domains through systematic scaling analysis.

Contribution

It provides the first comprehensive finite size scaling analysis of penetration depth data in Bi-2212 and YBCO, demonstrating the granular nature of these materials.

Findings

Finite size effects explain the tails in penetration depth temperature dependence.

Cuprates consist of nanoscale superconducting domains within a non-superconducting matrix.

The results support the granular model of high-temperature superconductors.

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.