Fabrication and Characterization of Short Josephson Junctions with Stepped Ferromagnetic Barrier

TL;DR

This paper reports the development of novel short Josephson junctions with stepped ferromagnetic barriers, enabling control over their ground state phase and potential for vortex-based magnetic flux states.

Contribution

It introduces a fabrication method for SIFS Josephson junctions with stepped ferromagnetic layers, allowing tunable 0 or pi ground states and exploration of vortex states.

Findings

Successfully fabricated stepped ferromagnetic barriers in Josephson junctions.

Demonstrated control over the junction ground state phase (0 or pi).

Identified potential for double degenerate ground states with vortex circulation.

Abstract

We present novel low-T_c superconductor-insulator-ferromagnet-superconductor (SIFS) Josephson junctions with planar and stepped ferromagnetic interlayer. We optimized the fabrication process to set a step in the ferromagnetic layer thickness. Depending on the thickness of the ferromagnetic layer the ground state of the SIFS junction has a phase drop of either 0 or pi. So-called 0-pi Josephson junctions, in which 0 and pi ground states compete with each other, were obtained. These stepped junctions may have a double degenerate ground state, corresponding to a vortex of supercurrent circulating clock- or counterclockwise and creating a magnetic flux which carries a fraction of the magnetic flux quantum \Phi_0. Here, we limit the presentation to static properties of short junctions.