Studies of the superconducting properties of YBCO/Ag/YBCO proximity junctions using a ceramic composite ring

Abstract We have studied the properties of YBCO/Ag/YBCO proximity interfaces in a Y 1 Ba 2 Cu 3 O 7−δ composite ring close to T c ; the junction critical current as a function of temperature (76–85K) and magnetic field (up to 50G). If a SNS junction is a part of a composite superconducting ring, the magnitude and relaxation of a macroscopic persistent current circulating around the ring provides a direct evidence that the junctions are really superconducting. We manufactured a SQUID-like ceramic ring containing two parallel SNS junctions and measured profiles of the trapped magnetic field due to the persistent current generated in the zero-field-cooled ring. The junction critical current was found to be in reasonable agreement with a formula for a SNS junction: I c (T)= I c ( O ) [1−(T/T c )] 2 .