Magnetic-field step response of a type-II superconductor as a simple test of the vortex bulk pinning

TL;DR

This study investigates the magnetic-field step response of a type-II superconductor slab to assess vortex bulk pinning by measuring induced electric fields and flux penetration, revealing that the vortex response aligns with bulk pinning being negligible except for surface effects.

Contribution

It demonstrates a simple experimental method to test vortex bulk pinning in type-II superconductors using magnetic-field step response measurements.

Findings

Vortex response matches ideal behavior with negligible bulk pinning.

Surface screening effects cause minor deviations from ideal response.

The method provides a straightforward test for vortex pinning properties.

Abstract

A slab in parallel field is submitted to a step-like magnetic-field excitation, of amplitude 1--10 G, in the same direction as the applied field. The slab has been rolled or spark cut, without special care, from a conventional superconductor ingot (lead-indium alloy), and its critical currents have standard values. The transitory electric field, induced on a face of the slab, has been measured. Thus, we obtain information about the magnetic flux penetrating and vortices entering the sample through this face. The only observed deviation from the ideal response is that magnetic-field diffusion being limited by surface screening, associated with a superficial critical-current density. Otherwise, the vortex array inside the slab responds exactly as if bulk pinning were ineffective.