Metastable inhomogeneous vortex configuration with non-uniform filling fraction inside a blind hole array patterned in a BSCCO single crystal and concentrating magnetic flux inside it

TL;DR

This study uses magneto-optical imaging to reveal a metastable, patchy vortex configuration with non-uniform filling fractions in a patterned BSCCO crystal, demonstrating how magnetic field pulses can reorganize flux and enhance shielding currents.

Contribution

It uncovers the existence of a metastable, non-uniform vortex state in a blind hole array and shows how magnetic pulses can control flux distribution and shielding currents.

Findings

Vortex configurations are patchy and metastable at low fields.

Magnetic pulses can reorganize vortices and enhance shielding currents.

Flux concentrates in the array center, preventing vortex entry.

Abstract

Using magneto-optical imaging technique, we map local magnetic field distribution inside a hexagonally ordered array of blind holes patterned in BSCCO single crystals. The nature of the spatial distribution of local magnetic field and shielding currents across the array reveals the presence of a non-uniform vortex configuration partially matched with the blind holes at sub-matching fields. We observe that the filling fraction is different in two different regions of the array. The mean vortex configuration within the array is described as a patchy vortex configuration with the patches having different mean filling fraction. The patchy nature of the vortex configuration is more pronounced at partial filling of the array at low fields while the configuration becomes more uniform with a unique filling fraction at higher fields. The metastable nature of this patchy vortex configuration is revealed by the application of magnetic field pulses of fixed height or individual pulses of varying height to the array. The metastability of the vortex configuration allows for a relatively easy way of producing flux reorganization and flux focusing effects within the blind hole array. Effect of the magnetic field pulses modifies the vortex configuration within the array and produces a uniform enhancement in the shielding current around the patterned array edges. The enhanced shielding current concentrates magnetic flux within the array by driving vortices away from the edges and towards the center of the array. The enhanced shielding current also prevents the uninhibited entry of vortices into the array. We propose that the metastable patchy vortex configuration within the blind hole array is due to a non-uniform pinning landscape leading to non-uniform filling of individual blind holes.