Area-dependence of spin-triplet supercurrent in ferromagnetic Josephson junctions

TL;DR

This study investigates how the critical current in ferromagnetic Josephson junctions depends on area, revealing different scaling behaviors in magnetized versus multi-domain samples, and supports a theoretical model predicting pi/2 coupling in as-grown samples.

Contribution

It provides experimental evidence on the area dependence of spin-triplet supercurrent in ferromagnetic Josephson junctions and compares different fabrication conditions.

Findings

Critical current scales linearly with area in magnetized junctions.

Multi-domain samples show mixed area dependence, sometimes sub-linear.

Results support the Zyuzin-Spivak theory predicting pi/2 coupling in as-grown samples.

Abstract

Josephson junctions containing multiple ferromagnetic layers can carry spin-triplet supercurrent under certain conditions. Large-area junctions containing multiple domains are expected to have a random distribution of 0 or pi coupling across the junction surface, whereas magnetized samples should have uniquely pi coupling everywhere. We have measured the area dependence of the critical current in such junctions, and confirm that the critical current scales linearly with area in magnetized junctions. For as-grown (multi-domain) samples, the results are mixed. Samples grown on a thick Nb base exhibit critical currents that scale sub-linearly with area, while samples grown on a smoother Nb/Al multilayer base exhibit critical currents that scale linearly with area. The latter results are consistent with a theoretical picture due to Zyuzin and Spivak that predicts that the as-grown samples should have global pi/2 coupling.