Josephson junctions with centered step and local variation of critical current density

TL;DR

This paper reports on the fabrication and analysis of Josephson junctions with a localized step in the critical current density, demonstrating how controlled etching affects junction properties and their diffraction patterns.

Contribution

It introduces a method to create Josephson junctions with a centered step in critical current density and validates the design through experimental and simulated diffraction patterns.

Findings

Uniform NiCu thickness confirmed by measurements

Good agreement between experimental and simulated diffraction patterns

Controlled etching maintains interface transparency

Abstract

Superconductor-insulator-ferromagnet-superconductor (SIFS) Josephson tunnel junctions based on Nb\Al2O3\Ni\Cu\Nb stacks with a thickness step in the metallic NiCu interlayer were fabricated. The step height of a few 0.1 nm was defined by optical lithography and controlled etching of both Nb and NiCu layers. Experimentally determined junction parameters by current-voltage characteristics and Fraunhofer pattern indicate a uniform NiCu thickness and similar interface transparencies for etched and non-etched parts. The critical current diffraction pattern was calculated and measured for stepped junctions having the same ground phase difference but different critical current densities in both halves. The measured data show a good agreement with simulations.