Pinning-induced formation of vortex clusters and giant vortices in mesoscopic superconducting disks

TL;DR

This paper reveals a new mechanism where pinning and disorder cause vortices in small superconducting disks to merge into clusters or giant vortices below critical temperature and field, differing from traditional vortex arrangements.

Contribution

It demonstrates that pinning-induced disorder can lead to the formation of vortex clusters and giant vortices in mesoscopic superconductors, a novel insight into vortex behavior.

Findings

Pinning causes vortices to merge into clusters or GVs.

Disorder-induced vortex merging occurs below Tc and Hc2.

Contrasts with vortex shells in clean samples.

Abstract

Multi-quanta, or giant, vortices (GVs) are known to appear in very small superconductors near the superconducting transition due to strong confinement of magnetic flux. Here we present evidence for a new, pinning-related, mechanism for the formation of GVs. Using Bitter decoration to visualise vortices in small Nb disks, we show that confinement in combination with strong disorder causes individual vortices to merge into clusters or even GVs well below Tc and Hc2, in contrast to well-defined shells of individual vortices found in the absence of pinning.