Structural disorder and critical voltage scaling in Al/AlOx/Al Josephson junction arrays

Abstract

The insulating state of one-dimensional Josephson junction (JJ) arrays is governed by collective charge dynamics and disorder-induced pinning, resulting in a finite critical voltage under dc bias. Here, we investigate the influence of fabrication-induced structural defects on the critical-voltage scaling of small-capacitance Aluminium-Aluminium oxide-Aluminium (Al/AlOx/Al) JJ arrays. Controlled variation of the aluminium evaporation rate produces pronounced changes in grain morphology and room-temperature junction resistance. Despite these substantial structural modifications, the normalised critical-voltage scaling is preserved, demonstrating that the collective transport behaviour is remarkably robust against this class of fabrication-induced defects. In contrast, the deliberate introduction of nanoscale gaps into the junctions introduces additional junction-to-junction structural variations that systematically modify the normalised scaling behaviour. Likewise, in situ postfabrication oxidation alters the scaling coefficient while preserving the functional form of the scaling law, indicating that the collective transport is sensitive to specific classes of structural modifications. These results establish which fabrication-induced structural defects influence the collective transport in insulating Al/AlOx/Al Josephson junction arrays, providing new insight into the role of fabrication-induced structural disorder and practical guidance for the design of future Quantum Phase Slip (QPS) devices.