Electrical Resistance Measurement Method To Investigate Superconducting Joints In Bi-2223 Tape

We studied a superconducting-joint technique for Bi-2223 tape (DI-BISCCO Type-H by Sumitomo Electric Industries Ltd.) used in the manufacture of superconducting devices such as magnetic shields, superconducting magnets, and SQUIDs (Super-conducting Quantum Interference Device). We fabricated a ring with a joint of Bi-2223 tape for application to a high-performance magnetic shield. It becomes important to suppress the resistance value of the joint as low as possible for superconducting devices. First, we attempted to estimate the resistance of the superconducting joint in our samples by measuring the decay of an induced ring current through a joint part. However, in this method, it was difficult to perform measurements with high accuracy due to long-term fluctuations in the environment's temperature, resulting in a maximum resolution on the order of 10-12. Here, we propose a new measurement method that leverages the superconducting properties of the joint to provide accurate measurements even in the presence of long-term fluctuations. Using this method, we conclude that the resistance of the joint was less than 10-13 for a small current at 77 K and that this result indicates that the superconducting-joint technique was successful.