Depinning of kinks in a Josephson-junction ratchet array

TL;DR

This paper investigates how trapped kinks in a Josephson-junction ratchet array depin under external current, revealing directional dependence and unique properties explained through experiments, simulations, and analytical models.

Contribution

It introduces a novel Josephson-junction ratchet array with alternating inductances and areas, and provides experimental, numerical, and analytical insights into kink depinning behavior.

Findings

Depinning current depends on current direction.

Depinning current exhibits long periodicity.

The system lacks reflection symmetry, explained analytically.

Abstract

We have measured the depinning of trapped kinks in a ratchet potential using a fabricated circular array of Josephson junctions. Our ratchet system consists of a parallel array of junctions with alternating cell inductances and junctions areas. We have compared this ratchet array with other circular arrays. We find experimentally and numerically that the depinning current depends on the direction of the applied current in our ratchet ring. We also find other properties of the depinning current versus applied field, such as a long period and a lack of reflection symmetry, which we can explain analytically.