Do columnar defects produce bulk pinning?

TL;DR

This study investigates whether columnar defects in YBaCuO superconductors enhance bulk vortex pinning, revealing that vortex motion is primarily surface-limited and bulk depinning occurs only at high fields.

Contribution

It demonstrates that in heavy-ion irradiated YBaCuO, vortex motion is surface-limited rather than bulk-pinned, challenging the assumption that columnar defects always produce bulk pinning.

Findings

Vortex motion is limited by surface nucleation of kinks.

Bulk depinning occurs only at fields above the matching field.

Vortex motion in the bulk involves kink sliding rather than pinning.

Abstract

From magneto-optical imaging performed on heavy-ion irradiated YBaCuO single crystals, it is found that at fields and temperatures where strong single vortex pinning by individual irradiation-induced amorphous columnar defects is to be expected, vortex motion is limited by the nucleation of vortex kinks at the specimen surface rather than by half-loop nucleation in the bulk. In the material bulk, vortex motion occurs through (easy) kink sliding. Depinning in the bulk determines the screening current only at fields comparable to or larger than the matching field, at which the majority of moving vortices is not trapped by an ion track.