Formation and Size-Dependence of Vortex Shells in Mesoscopic Superconducting Niobium Disks

TL;DR

This paper investigates how the size of mesoscopic superconducting niobium disks influences vortex shell formation, explaining experimental discrepancies by analyzing larger disks with theoretical models that include London screening effects.

Contribution

It provides a detailed analysis of vortex configurations in larger, mesoscopic and macroscopic Nb disks, incorporating London screening to explain experimental observations.

Findings

Vortex configurations depend strongly on disk radius.

Discrepancies with previous theories are due to size effects.

Identified stable vortex configurations matching experiments.

Abstract

Recent experiments [I.V. Grigorieva et al., Phys. Rev. Lett. 96, 077005 (2006)] on visualization of vortices using the Bitter decoration technique revealed vortex shells in mesoscopic superconducting Nb disks containing up to L=40 vortices. Some of the found configurations did not agree with those predicted theoretically. We show here that this discrepancy can be traced back to the larger disks with radii R ~ 1 to 2.5\mu m, i.e., R ~ 50-100\xi(0) used in the experiment, while in previous theoretical studies vortex states with vorticity L < 40 were analyzed for smaller disks with R ~ 5-20\xi(0). The present analysis is done for thin disks (mesoscopic regime) and for thick (macroscopic) disks where the London screening is taken into account. We found that the radius of the superconducting disk has a pronounced influence on the vortex configuration in contrast to, e.g., the case of parabolic confined charged particles. The missing vortex configurations and the region of their stability are found, which are in agreement with those observed in the experiment.