Electrical properties of superconducting joint between composite conductors

To investigate the electrical properties of the joint between superconducting multifilamentary wires, the authors used a radio-frequency superconducting quantum interference device (RF-SQUID) voltmeter to measure the extremely small voltage induced across the joint. They measured the time variation of both the current induced in a loop of superconducting wire and the voltage induced across the joint. A voltage sensitivity in the picovolt range was obtained with this apparatus. Comparisons of current decay between superconducting loops with soldered, spot-welded and cold-welded joints were made. A flux-creep-like phenomenon was seen in the current decay for the cold-welded and spot-welded joints.