Topologically protected superconducting ratchet effect generated by spin-ice nanomagnets

TL;DR

This paper demonstrates a superconducting ratchet device utilizing topologically frustrated spin-ice nanomagnets, which induces a unidirectional vortex flow through the interaction of superconducting vortices with magnetic half vortices.

Contribution

The work introduces a novel superconducting ratchet based on spin-ice nanomagnets, combining topology, magnetic charge distribution, and vortex interactions to achieve directed vortex motion.

Findings

The device exhibits a robust ratchet effect independent of magnetic charge distribution.

Superconducting vortices are driven unidirectionally by alternating forces.

The mechanism involves interaction with magnetic half vortices and Néel walls.

Abstract

We have designed, fabricated and tested a robust superconducting ratchet device based on topologically frustrated spin-ice nanomagnets. The device is made of a magnetic Co honeycomb array embedded in a superconducting Nb film. This device is based on three simple mechanisms: i) the topology of the Co honeycomb array frustrates in-plane magnetic configurations in the array yielding a distribution of magnetic charges which can be ordered or disordered with in-plane magnetic fields, following spin-ice rules, ii) the local vertex magnetization, which consists of a magnetic half vortex with two charged magnetic N\'eel walls, iii) the interaction between superconducting vortices and the asymmetric potentials provided by the N\'eel walls. The combination of these elements leads to a superconducting ratchet effect. Thus, superconducting vortices driven by alternating forces and moving on magnetic half vortices generate a unidirectional net vortex flow. This ratchet effect is independent of the distribution of magnetic charges in the array.