Threefold onset of vortex loops in superconductors with a magnetic core

TL;DR

This paper uses Ginzburg-Landau theory to show that magnetic inclusions in superconductors induce triplet vortex loops, leading to complex vortex configurations including surface-piercing vortex pairs.

Contribution

It reveals that vortex loops nucleate in triplets around magnetic cores and characterizes the resulting vortex structures in mesoscopic superconducting spheres.

Findings

Vortex loops nucleate in triplets around magnetic cores

Confined vortex loops coexist with surface-piercing vortex pairs

Complex vortex configurations emerge in superconductors with magnetic inclusions

Abstract

A magnetic inclusion inside a superconductor gives rise to a fascinating complex of {\it vortex loops}. Our calculations, done in the framework of the Ginzburg-Landau theory, reveal that {\it loops always nucleate in triplets} around the magnetic core. In a mesoscopic superconducting sphere, the final superconducting state is characterized by those confined vortex loops and the ones that eventually spring to the surface of the sphere, evolving into {\it vortex pairs} piercing through the sample surface.