Analysis of low-field isotropic vortex glass containing vortex groups in YBCO thin films visualized by scanning SQUID microscopy

TL;DR

This study visualizes and analyzes the vortex distribution in YBCO thin films, revealing an isotropic vortex glass with weak positional order and unusual vortex groups at higher magnetic fields.

Contribution

It provides the first detailed visualization and analysis of vortex arrangements in YBCO thin films, identifying vortex groups and characterizing the vortex glass state.

Findings

Weak short-range positional order in vortex distribution

Near-complete lack of orientational order

Observation of abnormally closely spaced vortex groups at higher fields

Abstract

The glass-like vortex distribution in pulsed laser deposited YBCO thin films is observed by scanning superconducting quantum interference device microscopy and analysed for ordering after cooling in magnetic fields significantly smaller than the Earth's field. Autocorrelation calculations on this distribution show a weak short-range positional order, while Delaunay triangulation shows a near-complete lack of orientational order. The distribution of these vortices is finally characterised as an isotropic vortex glass. Abnormally closely spaced groups of vortices, which are statistically unlikely to occur, are observed above a threshold magnetic field. The origin of these groups is discussed, but will require further investigation.