Geometry-related magnetic interference patterns in long SNS Josephson junctions

TL;DR

This study investigates how the geometry of the normal wire in long SNS Josephson junctions influences magnetic interference patterns, revealing a transition from Gaussian-like decay to Fraunhofer-like patterns and observing fractional Shapiro steps.

Contribution

It demonstrates the tunability of magnetic interference patterns in SNS junctions through wire geometry and provides a combined semiclassical and numerical modeling approach.

Findings

Transition from Gaussian-like to Fraunhofer-like patterns with geometry change

Observation of fractional Shapiro steps with slower decay

Numerical simulations accurately fit experimental data

Abstract

We have measured the critical current dependence on the magnetic flux of two long SNS junctions differing by the normal wire geometry. The samples are made by a Au wire connected to W contacts, via Focused Ion Beam assisted deposition. We could tune the magnetic pattern from the monotonic gaussian-like decay of a quasi 1D normal wire to the Fraunhofer-like pattern of a square normal wire. We explain the monotonic limit with a semiclassical 1D model, and we fit both field dependences with numerical simulations of the 2D Usadel equation. Furthermore, we observe both integer and fractional Shapiro steps. The magnetic flux dependence of the integer steps reproduces as expected that of the critical current Ic, while fractional steps decay slower with the flux than Ic.