The properties and potential applications of bulk RF SQUIDs made from YBaCuO, BiSrCaCuO and TlCaBaCuO

The authors have developed methods for making RF SQUIDs (superconducting quantum interference devices) from bulk samples of high-temperature ceramic superconductors. The technique relies on intrinsic closed superconducting pathways within the material to form the SQUID loop, and intergrain contact to provide the necessary Josephson elements. The material does not need to be multiply connected (for example, ring-shaped) or to have a region which is deliberately weakened or constricted. In this sense this type is quite unlike other RF SQUIDs that have been developed recently, which use break junctions or have machined constrictions. It is also much simpler to make and reveals some interesting properties related to the nature of the contact between grains. The authors conclude that a very simple system can make a magnetometer with a field sensitivity at 77 K of 1.5×10^-10 T-Hz^-1/2, comparable to that of a flux gate magnetometer. The technique also provides a good educational demonstration of quantum interference and can be used for detecting the superconducting state in small bulk samples