Strengthened proximity effect at grain boundaries to enhance inter-grain supercurrent in Ba1-K Fe2As2 superconductors

Iron-based superconductors have great potential for high-power applications due to their prominent high-field properties. One of the central issues in enhancing critical current density iron-based superconducting wires is reveal roles and limitations grain boundaries supercurrent transport. Here, we finely tuned electronic properties by doping Ba1-xKxFe2As2 a wide range (0.25<x<0.598). It found that intra-grain Jcintra peaks near x~0.287, while inter-grain Jcinter has maximum at about x~0.458. Remarkably, boundary transparency parameter defined as Jcinter/Jcintra rises monotonically with doping. Through detailed microscopic analysis, suggest FeAs segregation phase commonly existing adjacent grains constitute superconductor-normal metal-superconductor (SNS) Josephson junctions which play key role transporting supercurrent. A sandwich model based on proximity effect SNS junction proposed well interpret our data. overdoping largely strengthens consequently enhances intergrain Our results will shed new insights inspirations improving application parameters engineering.