Josephson transistor and robust supercurrent enhancement with spin-split superconductors

TL;DR

This paper theoretically explores how spin-split superconductors in a Josephson junction can significantly enhance supercurrent, especially under equilibrium conditions, and demonstrates control over supercurrent transitions via non-equilibrium driving and temperature bias.

Contribution

It reveals a robust supercurrent enhancement in long Josephson junctions with spin-split superconductors and introduces methods to control supercurrent transitions using non-equilibrium conditions.

Findings

Supercurrent can be enhanced by over 100% with increased spin-splitting.

Efficient $\pi$-transition achieved with lower transition voltage under non-equilibrium conditions.

Temperature bias suppresses supercurrent, causing sharp jumps in supercurrent output.

Abstract

We theoretically investigate the supercurrent flow in a Josephson junction consisting of two spin-split superconductors combined by a normal metal weak link. The normal metal may be driven out of equilibrium, thus modifying the electron and hole occupation and consequently the supercurrent through the system. Considering first an equilibrium normal metal, we find that increasing the spin-splitting field can enhance the supercurrent strongly for long junctions at low temperatures. In contrast to previous work, this is a much larger enhancement (over 100%) and it is achieved for both parallel and antiparallel spin-splitting field configurations, making the effect robust. On the other hand, when a gate voltage is applied to drive the system out of equilibrium, we demonstrate a more efficient $\pi$-transition of the supercurrent in terms of a lower transition voltage by tuning the spin-splitting. Moreover, we find the application of temperature bias strongly suppresses the supercurrent, resulting in very sharp supercurrent jumps as outputs.