Spin-switch Josephson junctions with magnetically tunable $\sin(\delta\varphi/n)$ shape

TL;DR

This paper proposes a magnetic field-tunable Josephson junction with multiple superconductors that can switch between different current-phase relations, enabling a highly controllable supercurrent switch with potential applications in quantum devices.

Contribution

It introduces a novel Josephson junction design with tunable current-phase relations, including the $ ext{sin}(rac{ ext{delta} ext{phi}}{n})$ shape, and demonstrates its switching capabilities and generalization to arbitrary n.

Findings

The $ ext{sin}(rac{ ext{delta} ext{phi}}{2})$-shaped relation remains $2 ext{pi}$-periodic despite interface asymmetries.

Switching between $ ext{sin}( ext{delta} ext{phi})$ and $ ext{sin}(rac{ ext{delta} ext{phi}}{2})$ achieves over two orders of magnitude change in supercurrent.

The approach can be extended to $ ext{sin}(rac{ ext{delta} ext{phi}}{n})$ relations for arbitrary integers n.

Abstract

With a combination of simple analytical arguments and extensive numerical simulations, we theoretically propose a Josephson junction with $n+1$ superconductors where the current-phase relation can be toggled in situ between a $\sin(\delta\varphi)$ and $\sin(\delta\varphi/n)$ shape using an applied magnetic field. Focusing in particular on the case $n=2$, we show that by using realistic system parameters such as unequal interface transparencies, the $\sin(\delta\varphi/2)$-shaped solution retains its $2\pi$-periodicity due to discontinuities at $\delta\varphi = \pm \pi$. Moreover, we demonstrate that as one toggles between the $\sin(\delta\varphi)$- and $\sin(\delta\varphi/2)$-shaped solutions, the system acts as an on--off switch, and can acheive more than two orders of magnitude difference between the supercurrent in the on and off states. Finally, we argue that the same approach can be generalized to switchable $\sin(\delta\varphi/n)$ junctions for arbitrary integers~$n$, which we motivate by analytically solving the Josephson equations for double- and triple-barrier junctions.