Columnar defects and vortex fluctuations in layered superconductors

TL;DR

This paper explores how columnar defects influence vortex fluctuations in layered superconductors, revealing increased interlayer coupling and shifts in decoupling behavior due to defect-induced suppression of thermal fluctuations.

Contribution

It provides a detailed analysis of vortex behavior near columnar defects, including thermodynamics, creep regimes, and the impact on decoupling lines, which was not previously characterized.

Findings

Columnar defects increase interlayer Josephson coupling.

Thermal fluctuations of pancakes are suppressed by defects.

Decoupling line shifts upward around the matching field.

Abstract

We investigate fluctuations of Josephson-coupled pancake vortices in layered superconductors in the presence of columnar defects. We study the thermodynamics of a single pancake stack pinned by columnar defects and obtain the temperature dependence of localization length, pinning energy and critical current. We study the creep regime and compute the crossover current between line-like creep and pancake-like creep motion. We find that columnar defects effectively increase interlayer Josephson coupling by suppressing thermal fluctuations of pancakes. This leads to an upward shift in the decoupling line most pronounced around the matching field.