Metal-oxide ceramic RF SQUID operating at 77 K

The authors fabricated several versions of Zimmerman-type RF SQUIDs (superconducting quantum interference devices) from bulk ceramic YBa₂Cu₃O_x samples and studied their characteristics. The SQUIDs operated reliably at liquid nitrogen temperature and proved to be stable over time. Some of their properties were similar to those of RF SQUIDs based on conventional superconductors, but there were also some major distinctions. The latter may be due to the fact that because of the macroscopic size of the weak link, the magnetic flux vortex enters reversibly (without respect to the RF current) the body of the weak link without crossing it. One of the SQUIDs operated as a conventional nonhysteretic SQUID, but the small value of the critical current of the weak link led to a lower operating temperature (T≲60 K)