Switching device for the superconducting phase transition measurements of thin W films using a single superconducting quantum interference device

A simple superconducting switch has been developed for the measurements of the low temperature superconducting phase transitions of several thin W samples connected simultaneously to a single superconducting quantum interference device. The switch, based on a Ti thin film resistor, can be set to normal or to superconducting within the cryostat by adjusting its temperature above or below the transition temperature by means of a thin film heater. The experimental setup, circuit and device properties, are discussed in detail. As an example of its application the superconducting phase transitions of two thin W samples on sapphire connected in series were measured subsequently as a function of temperature by applying two switches connected parallel to the samples. The switches exhibited a resistance of 67 Ω–1 kΩ at 4 K depending on the thickness and geometry of the Ti film and on the substrate material. The deviation from the real electrical resistance value of the samples caused by the finite resistance of the switches was found to be a maximum of $6×10−6$ Ω. This, compared to the resistances to be measured (about $2×10−2$ Ω), we consider negligible. The application of several switches within a cryostat can multiply the number of specimens measured in the same cooling cycle, enabling a more efficient characterization of the cryogenic properties of superconducting specimens.