Shapiro-step identifiability in YBCO Josephson weak links: A branch-paired reanalysis

An RF-driven Josephson weak link can retain a measurable response maximum after that maximum ceases to identify the first Shapiro-step voltage. We reanalyse archived antenna-coupled YBCO measurements using a branch-paired, continuity-aware framework that separates symmetric voltage detuning from common-mode offset and permits an explicit non-identifiable outcome. The source archive comprises 181 TXT entries; the preserved analysis cohort contains 134 distinct RF-exposed records. At 155 GHz, Device A retains paired errors of 0.467–0.539% from 10 to 50 K, develops a 3.481% paired displacement at nominal 60 K, and yields no defensible first-step assignment in ten standard-frequency records at nominal 70 K despite persistent maxima. Device B remains identifiable at all 15 nominally matched temperature–frequency conditions and in 14/14 available nominal-70 K RF records (0.560% RMS error). Across 20 documented sensitivity settings, the broad condition-level interpretation is maintained, with two isolated false-positive acceptances under stress settings. A constrained overlapping-response reconstruction reproduces the displaced maximum, while fits to native acquired I–V samples also admit a flexible asymmetric single-response description; the microscopic decomposition is not identified. The results establish a practical distinction between detecting a maximum and assigning an identifiable Shapiro-step voltage, while documenting the uncertainty and configuration-comparison limits of the historical measurements.