Ultra-fast vortex motion in dirty Nb-C superconductor with a close-to-perfect edge barrier

TL;DR

This study demonstrates ultra-fast vortex motion in a Nb-C superconductor with a near-perfect edge barrier, revealing new insights into flux-flow instability suppression and potential applications in fast photon detection.

Contribution

It provides experimental evidence of ultra-fast vortex velocities in Nb-C superconductor and introduces an edge-controlled FFI model describing the spatial evolution of vortex dynamics.

Findings

Vortex velocities of 10-15 km/s achieved.

Edge barrier orders vortex motion at high currents.

Nb-C identified as promising for fast single-photon detectors.

Abstract

The ultra-fast dynamics of superconducting vortices harbors rich physics generic to nonequilibrium collective systems. The phenomenon of flux-flow instability (FFI), however, prevents its exploration and sets practical limits for the use of vortices in various applications. To suppress the FFI, a superconductor should exhibit a rarely achieved combination of properties: weak volume pinning, close-to-depairing critical current, and fast heat removal from heated electrons. Here, we demonstrate experimentally ultra-fast vortex motion at velocities of 10-15 km/s in a directly written Nb-C superconductor in which a close-to-perfect edge barrier orders the vortex motion at large current values. The spatial evolution of the FFI is described using the edge-controlled FFI model, implying a chain of FFI nucleation points along the sample edge and their development into self-organized Josephson-like junctions (vortex rivers). In addition, our results offer insights into the applicability of widely used FFI models and suggest Nb-C to be a good candidate material for fast single-photon detectors.