A simple technique for measuring the transition temperature at microwave frequencies

A technique is described which enables contactless measurements at microwave frequencies of the superconducting transition. The approach employs an electrically small microwave loop antenna to sense the change in the reflected microwave signal as flux is expelled, due to the Meissner effect, from the superconductor. Advantages of this technique include the ability to measure small areas of a superconducting thin film after photolithographic patterning into a device geometry. This approach is very sensitive in the frequency range from 0.05 GHz to 5 GHz and for some YBCO films a dependence of the transition temperature width on frequency has been observed. Such frequency-dependent signatures may provide valuable information regarding improvements in film deposition and device processing.