Scanning SQUID Imaging of Diamagnetism in Proximity Coupled Niobium Nano-Island Arrays on Gold

The effects of disorder can play an important role in the superconductivity of two dimensional materials. Understanding disorder in 2D superconductors can help elucidate the nature of a variety of quantum critical transitions, including the superconductor-insulator transition. Here we present studies of proximity coupled niobium island arrays on gold with engineered disorder that can serve as model systems for disordered 2D superconductors. Local susceptibility measurements via Scanning SQUID Microscopy (SSM) show that the local diamagnetic response of the arrays is inhomogeneous and can be tuned by changing the landscape of island positions. In contrast to previous transport studies that showed that ordered proximity-coupled superconducting island arrays can be well-described as a single Josephson junction, Josephson simulations suggest that the superconducting response of our disordered arrays cannot be fully explained by a junction array model. Our work suggests new directions for studying a wider parameter space of disorder in 2D superconducting materials and motivates future experiments with more exotic materials.