Vortex interaction in thin films -- a crossover from type I to type II superconductivity

TL;DR

This paper explores how vortex interactions in thin superconducting films transition from type I to type II behavior, influenced by material properties and film thickness, revealing complex interaction profiles and vortex chain formations.

Contribution

It introduces a combined formalism to analyze vortex interactions in thin films, accounting for stray magnetic fields and material variations, highlighting qualitative differences from bulk vortex interactions.

Findings

Stray fields cause long-range repulsive vortex interactions.

Vortex interactions show complex attraction-repulsion behavior.

Vortex chains are explained by the interaction profiles.

Abstract

Interactions between vortices in thin superconducting films are investigated in the crossover (intertype) regime between superconductivity types I and II. We consider two main factors responsible for this crossover: a) changes in the material characteristics of the film and b) variations of the film thickness controlling the effect of the stray magnetic fields outside superconducting sample. The analysis is done within the formalism that combines the perturbation expansion of the microscopic equations to one order beyond the Ginzburg-Landau theory with the leading contribution of the stray fields. It is shown that the latter gives rise to qualitatively different spatial profile and temperature dependence of the vortex interaction potential, as compared to bulk vortex interactions. The resulting interaction is long-range repulsive while exhibiting complex competition of attraction and repulsion at small and intermediate separations of vortices. This explains the appearance of vortex chains reported earlier for superconducting films.