Revealing Nanoscale Inhomogeneities in a Superconducting Nanowire through Self-Heating Hotspot Scanning and Mapping

The pursuit of uniform superconducting nanowires is crucial for the advancement of superconducting devices. However, inhomogeneities, typically on the order of the coherence length, significantly affect macroscopic superconducting phenomena. The lack of precise information regarding their locations, quantities, and direct impact on the device performance hinders the understanding of superconducting switching mechanisms and limits further performance optimization. In this study, a hotspot scanning microscope was developed to locate inhomogeneities with nanoscale resolution and reveal their spatial distribution. Along a 12-μm-long and nominally uniform superconducting nanowire, 50 distinct IV curves were observed, indicating the presence of a substantial number of inhomogeneities. Among these, three dark-count sources were identified with a minimum separation of 0.7 μm, and their individual contributions were quantitatively extracted. This work demonstrates the ubiquitous presence of inhomogeneities and clarifies their influence on the device performance, providing a foundation for future optimization and engineering efforts.