# Finite-size effect of critical penetration of Pearl vortices in narrow superconducting flat rings

## TL;DR

This study investigates the finite-size effects on the critical magnetic field required for Pearl vortices to penetrate narrow superconducting rings, revealing a size-dependent threshold field that influences vortex trapping.

## Contribution

It provides a quantitative relationship between the threshold penetration field and the ring width, enhancing understanding of vortex behavior in mesoscopic superconducting structures.

## Key findings

- Vortices are excluded below a threshold field $H_p$.
- $H_p$ scales inversely with the square of the ring width.
- The relationship $H_p = 1.9 \u00b1 0.1 \, _0/w_{ring}^2$ is established.

## Abstract

We revisit the critical penetration of Pearl vortices in narrow superconducting flat rings cooled in magnetic fields. Scanning superconducting quantum interference device microscopy measurements showed how magnetic field penetrates and vortices are trapped in flat rings made of amorphous MoGe thin films. Counting the number of trapped vortices for each image, we found that the vortices are completely excluded from the ring annulus when the applied field $H$ is below a threshold field $H_{\rm{p}}$: Above this field, the vortices increase linearly with field. The obtained values of $H_{\rm{p}}$ depend on the annulus width $w_{\rm{ring}}$ and follow the relation $\mu_0H_{\rm{p}} = (1.9 \pm 0.1) \Phi_0/w_{\rm{ring}}^2$ with the superconducting flux quantum $\Phi_0$. This relationship provides an insight into the effect of the net-current circulating in the annular region, and also leads to a precise control to trap or eliminate vortices in flat rings.