Oral Presentation

Broken IV Curves Problem and Its Possible Reason (Remote)

Author(s): Wenlei Shan and Shohei Ezaki (NAOJ)

Presenter: Wenlei Shan (National Astronomical Observation, Japan)

Anomalous bending, or “broken” current–voltage characteristics (IVCs), is frequently observed in superconductor–insulator–superconductor (SIS) junctions operated at high current density. This behavior is attributed to localized self-heating near the junction. The resulting temperature rise reduces the critical current of nearby weak links, making them visible in IVC measurements. To analyze the self-heating mechanism, finite-element simulations were conducted to evaluate the steady-state temperature distribution, explicitly incorporating the temperature dependence of thermal conductivities, interfacial resistances, and substrate materials. A heating coefficient extracted from the simulations was then applied to an IVC model that includes temperature-dependent gap energy and quasiparticle broadening. The simulated IVCs successfully reproduced the measured bending features, confirming that the broken IVCs originate from self-heating. The analysis further indicates that when a weak link exists near the junction, it can reach its critical temperature at the bending bias, providing a consistent physical explanation for the observed anomaly.