Reducing vortex density in superconductors using the ratchet effect

TL;DR

This paper demonstrates that applying an ac current to superconductors with asymmetric pinning patterns induces vortex motion via the ratchet effect, potentially enabling vortex removal and improving superconductor device performance.

Contribution

It introduces a novel method using the ratchet effect to actively remove vortices from superconductors, which is a new approach compared to traditional pinning techniques.

Findings

Ratchet effect induces vortex motion in superconductors.

Asymmetric pinning patterns control vortex direction.

Potential for vortex removal in low-temperature superconductors.

Abstract

A serious obstacle that impedes the application of low and high temperature superconductor (SC) devices is the presence of trapped flux. Flux lines or vortices are induced by fields as small as the Earth's magnetic field. Once present, vortices dissipate energy and generate internal noise, limiting the operation of numerous superconducting devices. Methods used to overcome this difficulty include the pinning of vortices by the incorporation of impurities and defects, the construction of flux dams, slots and holes and magnetic shields which block the penetration of new flux lines in the bulk of the SC or reduce the magnetic field in the immediate vicinity of the superconducting device. Naturally, the most desirable would be to remove the vortices from the bulk of the SC. There is no known phenomenon, however, that could form the basis for such a process. Here we show that the application of an ac current to a SC that is patterned with an asymmetric pinning potential can induce vortex motion whose direction is determined only by the asymmetry of the pattern. The mechanism responsible for this phenomenon is the so called ratchet effect, and its working principle applies to both low and high temperature SCs. As a first step here we demonstrate that with an appropriate choice of the pinning potential the ratchet effect can be used to remove vortices from low temperature SCs in the parameter range required for various applications.