On the large role of weak uncorrelated pinning introduced by BZO nanorods at low temperatures in REBCO thin films

TL;DR

This study reveals that in REBCO thin films with BZO nanorods, weak uncorrelated pinning plays a significant role at low temperatures, contrasting with the dominant correlated pinning observed at higher temperatures.

Contribution

The paper demonstrates the increasing importance of weak uncorrelated pinning at low temperatures in REBCO films with BZO nanorods, challenging previous focus on correlated pinning effects.

Findings

Correlated c-axis pinning diminishes at lower temperatures.

Weak uncorrelated pinning becomes dominant below 77 K.

Pinning behavior varies significantly with temperature and field orientation.

Abstract

REBa$_{2}$Cu$_{3}$O$_{x}$ films can achieve remarkably high critical current density values by the incorporation of insulating nanoparticles. A particular interesting case concerns BaZrO$_{3}$ (BZO) nanorods, whose strongly correlated effect is seen at high temperatures. Here we investigate the field, temperature and angular dependence of the critical current density over a wide temperature range from 4.2 K to 77 K, and magnetic fields up to 31 T. We show that the correlated c-axis pinning of BZO nanorods becomes progressively less obvious at lower temperature. Indeed at 4.2 K and fields up to 31 T, the only correlated pinning is for fields parallel to the film plane. We interpret the change as being due to significant contributions from dense but weak pins that thermal fluctuations render ineffective at high temperatures but which become strong at lower temperatures.