Experimental study of the correlation length of critical-current fluctuations in the presence of surface disorder: Probing vortex long-range interactions

TL;DR

This study investigates how surface disorder affects vortex fluctuations and critical currents in Niobium superconductors, revealing that long-range vortex interactions can extend correlation lengths influenced by surface topography.

Contribution

It demonstrates the impact of surface modifications on vortex fluctuation correlation lengths and critical currents, highlighting the role of long-range interactions in superconducting vortex behavior.

Findings

Surface disorder modifies critical current and noise.

Correlation length linked to surface topography.

Long-range interactions extend correlation length.

Abstract

We report on critical currents and voltage noise measurements in Niobium strips in the superconducting state, in the presence of a bulk vortex lattice ($B < B_{C2}$) and in the surface superconducting state ($B_{c2}< B < B_{C3}$). For homogeneous surfaces, the correlation length of the current fluctuations can be associated with the electromagnetic skin depth of vortex superficial instabilities. The modification of the surface state by means of low energy irradiation induces a strong modification of the critical current and of the noise. The appearance of a corner frequency in the spectral domain can be linked with the low wave-vectors of the artificial corrugation. Since this latter occurs only for $B < B_{C2}$, we propose that the long-range interactions allow the correlation length to extend up to values imposed by the surface topography.