Mobile fluxons as coherent probes of periodic pinning in superconductors

TL;DR

This paper demonstrates that fluxons in superconductors can serve as coherent, mobile probes to non-destructively analyze periodic pinning potentials, revealing insights into vortex-nanostructure interactions.

Contribution

It introduces a novel method using fluxon dynamics under microwave and dc currents to map the pinning potential in superconductors with artificial nanostructures.

Findings

Fluxons act as mobile probes of the pinning potential.

Voltage responses can be fitted to deduce the potential landscape.

Pinning is primarily caused by vortex length reduction.

Abstract

The interaction of (quasi)particles with a periodic potential arises in various domains of science and engineering, such as solid-state physics, chemical physics, and communication theory. An attractive test ground to investigate this interaction is represented by superconductors with artificial pinning sites, where magnetic flux quanta (Abrikosov vortices) interact with the pinning potential $U(r) = U(r + R)$ induced by a nanostructure. At a combination of microwave and dc currents, fluxons act as mobile probes of $U(r)$: The ac component shakes the fluxons in the vicinity of their equilibrium points which are unequivocally determined by the local pinning force counterbalanced by the Lorentz force induced by the dc current, linked to the curvature of $U(r)$ which can then be used for a successful fitting of the voltage responses. A good correlation of the deduced dependences $U(r)$ with the cross sections of the nanostructures points to that pinning is primarily caused by vortex length reduction. Our findings pave a new route to a non-destructive evaluation of periodic pinning in superconductor thin films. The approach should also apply to a broad class of systems whose evolution in time can be described by the coherent motion of (quasi)particles in a periodic potential.