Continuum versus discrete flux behaviour in large mesoscopic Bi(2)Sr(2)CaCu(2)O(8+delta) disks

TL;DR

This study investigates flux behavior in large mesoscopic Bi(2)Sr(2)CaCu(2)O(8+delta) disks, revealing the transition from discrete vortex structures to continuum flux distributions through experimental measurements and numerical simulations.

Contribution

It provides a detailed comparison of experimental flux distributions with analytic models and simulations, defining the crossover lengthscale between discrete and continuum vortex behaviors.

Findings

Discrete vortex signatures observed at low fields

Continuum flux behavior fits analytic models

Crossover lengthscale between regimes identified

Abstract

Scanning Hall probe and local Hall magnetometry measurements have been used to investigate flux distributions in large mesoscopic superconducting disks with sizes that lie near the crossover between the bulk and mesoscopic vortex regimes. Results obtained by directly mapping the magnetic induction profiles of the disks at different applied fields can be quite successfully fitted to analytic models which assume a continuous distribution of flux in the sample. At low fields, however, we do observe clear signatures of the underlying discrete vortex structure and can resolve the characteristic mesoscopic compression of vortex clusters in increasing magnetic fields. Even at higher fields, where single vortex resolution is lost, we are still able to track configurational changes in the vortex patterns, since competing vortex orders impose unmistakable signatures on "local" magnetisation curves as a function of the applied field. Our observations are in excellent agreement with molecular dynamics numerical simulations which lead us to a natural definition of the lengthscale for the crossover between discrete and continuum behaviours in our system.