Weak Link Point Contact Devices

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Abstract
Recent progress in our laboratory on permanently adjusted niobium point-contact superconducting devices is reported. We describe an rf noise-biased magnetometer obtained by appropriate tuning and adjustment of the point contact in a superconducting ring that is coupled to an LC tank circuit which provides an rf noise-bias excitation at its resonant frequency. Thus, the rf oscillator normally used is eliminated although the magnetometer noise increases somewhat. In addition, mechanically stable, room-temperature-helium-temperature-cyclable insulated double and single point contacts have been obtained by use of an insulating glass with thermal expansion matching that of niobium. When two of these contacts are connected in parallel the resultant device works quite well as a cyclable dc-biased magnetometer. Study of the temperature dependence of the critical current is facilitated by the stable configuration. Preliminary measurements showed sharp rises of the critical current with decreasing temperature similar to those observed with S-N-S sandwiches. Properties of these devices are discussed.

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