Continuum vs. discrete flux behaviour in large mesoscopic Bi₂Sr₂CaCu₂O₈₊ disks

¹  Department of Physics, University of Bath - Claverton Down, Bath, BA2 7AY, UK, EU
²  Departement Fysica, Universiteit Antwerpen - Groenenborgerlaan 171, B-2020 Antwerpen, Belgium, EU
³  Ames Laboratory, Department of Physics and Astronomy, Iowa State University - Ames, IA 50011-3160, USA
⁴  Department of Applied Physics, The University of Tokyo - Hongo, Bunkyo-ku, Tokyo 113-8656, Japan

Corresponding author: Milorad.Milosevic@ua.ac.be

Received: 3 July 2008
Accepted: 22 November 2008

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.