Long-Range Superharmonic Josephson Current

TL;DR

This paper investigates long-range superharmonic Josephson currents in superconductor-ferromagnet-superconductor junctions with a spin-active region, revealing that two Cooper pairs dominate transport at low temperatures, leading to a superharmonic current-phase relation.

Contribution

It demonstrates that in such junctions, only a pair of Cooper pairs can propagate long-range, resulting in a superharmonic current-phase relation at low temperatures.

Findings

Superharmonic current-phase relation $I ightarrow ext{sin}2 extphi$ identified.

Long-range propagation of only two Cooper pairs in the presence of a single spin-active region.

Dominant coherent transport process at temperatures below the Thouless energy.

Abstract

We consider a long superconductor-ferromagnet-superconductor junction with one spin-active region. It is shown that an \textit{odd} number of Cooper pairs cannot have a long-range propagation when there is \textit{only one} spin-active region. When temperature is much lower than the Thouless energy, the coherent transport of \textit{two} Cooper pairs becomes dominant process and the \textit{superharmonic} current-phase relation is obtained ($I\propto\sin2\phi$).