Detection of discretized single-shell penetration in mesoscopic vortex matter

Abstract

We investigated configurational changes in mesoscopic vortex matter with less than thousand vortices during flux penetration in freestanding 50 $\mu$m diameter disks of Bi${}_2$Sr${}_2$CaCu${}_2$O${}_{8+\delta }$. High-resolution AC and DC local magnetometry data reveal oscillations in the transmittivity echoed in peaks in the third-harmonics magnetic signal fainting on increasing vortex density. By means of extra experimental evidence and a simple geometrical analysis we show that these features fingerprint the discretized entrance of single-shells of vortices having a shape that mimics the sample edge.