Current density inhomogeneity throughout the thickness of superconducting films and its effect on their irreversible magnetic properties

TL;DR

This paper investigates how current density varies across the thickness of superconducting films and how this inhomogeneity influences their magnetic properties, introducing a new model that explains experimental observations.

Contribution

The authors develop a new critical state model accounting for current density inhomogeneity across film thickness, enhancing understanding of magnetic behavior in superconducting films.

Findings

Current density is inhomogeneous on the scale of the inter vortex distance.

Surface pinning significantly enhances current density inhomogeneity.

The new model explains the thickness dependence of current density and magnetic relaxation.

Abstract

We calculate the distribution of the current density $j$ in superconducting films along the direction of an external field applied perpendicular to the film plane. Our analysis reveals that in the presence of bulk pinning $j$ is inhomogeneous on a length scale of order the inter vortex distance. This inhomogeneity is significantly enhanced in the presence of surface pinning. We introduce new critical state model, which takes into account the current density variations throughout the film thickness, and show how these variations give rise to the experimentally observed thickness dependence of $% j$ and magnetic relaxation rate.