Local imaging of diamagnetism in proximity coupled niobium nano-island arrays on gold thin films

TL;DR

This study investigates how engineered disorder affects the local magnetic response of proximity-coupled niobium nano-island arrays on gold films, using scanning SQUID measurements and a Josephson junction network model.

Contribution

It introduces a model for the static magnetic response of disordered 2D superconducting arrays and compares it with experimental SQUID data, highlighting the effects of inhomogeneity and dissipation.

Findings

Disordered arrays show inhomogeneous diamagnetic response.

The junction network model describes low-field behavior well.

Dissipation and vortex motion affect high-field response.

Abstract

In this work we study the effect of engineered disorder on the local magnetic response of proximity coupled superconducting island arrays by comparing scanning Superconducting Quantum Interference Device (SQUID) susceptibility measurements to a model in which we treat the system as a network of one-dimensional (1D) superconductor-normal metal-superconductor (SNS) Josephson junctions, each with a Josephson coupling energy $E_J$ determined by the junction length or distance between islands. We find that the disordered arrays exhibit a spatially inhomogeneous diamagnetic response which, for low local applied magnetic fields, is well described by this junction network model, and we discuss these results as they relate to inhomogeneous two-dimensional (2D) superconductors. Our model of the static magnetic response of the arrays does not fully capture the onset of nonlinearity and dissipation with increasing applied field, as these effects are associated with vortex motion due to the dynamic nature of the scanning SQUID susceptometry measurement. This work demonstrates a model 2D superconducting system with engineered disorder and highlights the impact of dissipation on the local magnetic properties of 2D superconductors and Josephson junction arrays.