Unconventional Temperature-Dependent Critical Current in the Fe-Based Hybrid Josephson Junction with a Metallic Barrier

We use the multiband Fe-based superconductor (FeSC) Ba_0.5K_0.5Fe₂As₂ and the conventional superconductor Nb to fabricate a hybrid Josephson junction where an Al layer serves as a highly transparent barrier. Detailed electrical transportations are studied including the Shapiro steps and the Fraunhofer-like pattern, which indicate strong Josephson effects. An unusual temperature-dependent critical current was observed, which cannot be well described by the conventional Ambegaokar–Baratoff relation. We utilize a model considering both multiband properties in the FeSC and the conventional superconductor/normal metal/superconductor Josephson junction theory, proving that this temperature dependence on critical current is attributed to the barrier transparency of the Josephson junction. We hope our studies can be a reference for the applications or physics research of FeSC Josephson junctions.