Mesoscopic effects in superconductor-ferromagnet-superconductor junctions

TL;DR

This paper investigates the behavior of supercurrents in superconductor-ferromagnet-superconductor junctions at zero temperature, revealing non-exponential decay, sample-specific phase, and a ground state phase difference of ±π/2 in large-area junctions.

Contribution

It demonstrates that supercurrents do not decay exponentially with junction thickness and identifies the sample-specific phase behavior and ground state phase difference in mesoscopic and large-area junctions.

Findings

Supercurrent does not decay exponentially with junction thickness.

The supercurrent's sign is sample-specific and can change with temperature.

Large-area junctions have a ground state phase difference of ±π/2.

Abstract

We show that at zero temperature the supercurrent through the superconductor - ferromagnetic metal - superconductor junctions does not decay exponentially with the thickness $L$ of the junction. At large $L$ it has a random sample-specific sign which can change with a change in temperature. In the case of mesoscopic junctions the phase of the order parameter in the ground state is a random sample-specific quantity. In the case of junctions of large area the ground state phase difference is $\pm \pi/2$.