Finite-size and pressure effects in YBa_2Cu_4O_8 probed by magnetic field penetration depth measurements

TL;DR

This study investigates how finite-size effects and pressure influence the magnetic penetration depth in YBa_2Cu_4O_8, revealing nanoscale domains and questioning the existence of a fully coherent macroscopic superconducting phase.

Contribution

It provides the first detailed analysis of pressure and finite-size effects on penetration depth in this cuprate, highlighting nanoscale granularity and its implications.

Findings

Nanoscale domains with sizes 28.9-33.2 Å identified

Finite-size scaling reveals granular nature of the material

Pressure affects domain size but challenges macroscopic coherence

Abstract

We explore the combined pressure and finite-size effects on the in-plane penetration depth \lambda_{ab} in YBa_2Cu_4O_8. Even though this cuprate is stoichiometric the finite-size scaling analysis of \lambda_{ab}^{-2}(T) uncovers the granular nature and reveals domains with nanoscale size L_{c} along the c-axis. L_{c} ranges from 33.2 Angstrom to 28.9 Angstrom at pressures from 0.5 to 11.5 kbar. These observations raise serious doubts on the existence of a phase coherent macroscopic superconducting state in cuprate superconductors.