Effect of nanosize BaZrO3 inclusions on vortex parameters in YBaCuO

TL;DR

This study investigates how nanosize BaZrO3 inclusions affect vortex behavior in YBaCuO superconducting films, revealing a pinning regime change and increased vortex viscosity with higher BaZrO3 content.

Contribution

It introduces a detailed analysis of vortex parameters in YBaCuO with BaZrO3 inclusions, highlighting a crossover in pinning mechanisms between 2.5% and 5% BaZrO3 content.

Findings

Pinning regime changes between 2.5% and 5% BaZrO3.

Vortex viscosity increases with magnetic field.

Vortices occupy both BaZrO3 sites and interstitials.

Abstract

We report on the field dependence of the microwave complex resistivity data in YBa$_2$Cu$_3$O$_{7-x}$/BaZrO$_3$ films grown by PLD at various BaZrO$_3$ content. The data, analyzed within a recently developed general framework for the mixed-state microwave response of superconductors, yield the field dependence of the fluxon parameters such as the vortex viscosity and the pinning constant. We find that pinning undergoes a change of regime when the BaZrO$_3$ content in the target increases from 2.5 mol.% to 5 mol.%. Simultaneously, the vortex viscosity becomes an increasing function of the applied magnetic field. We propose a scenario in which flux lines are pinned as bundles, and a crossover from dilute point pins to dense c-axis correlated defects takes place between 2.5 and 5 mol.% in the BZO concentration. Our data are inconsistent with vortices occupying mainly the BaZrO$_3$ sites at low fields, and suggest instead that vortices occupy both BaZrO$_3$ sites and interstitials in the YBa$_2$Cu$_3$O$_{7-x}$ matrix, even at low fields.