Coaxial Millimeter Wave Josephson Junction Detector

We describe a novel Josephson device made from a section of superconducting (niobium) coaxial line and from thin superconducting (lead) membrane mounted perpendicularly to line axis. The membrane makes good galvanic contact with the outer coaxial conductor and forms a circumferential Josephson junction with the (oxidized) center conductor. This configuration as compared to the traditional planar one couples better to microwave fields and is self-screened against magnetic disturbances. The device has the stability of a good permanently-adjusted point-contact and, so far, exhibits only weak-link type Josephson behaviour. Lack of true tunnelling is attributed to imperfect surface finish of the central conductor. The device has been successfully tested as broadband detector at 78 GHz.