TEMPERATURE-DEPENDENCE OF SURFACE IMPEDANCE OF PULSED-LASER-DEPOSITEDYBCO FILMS

One promising application of HTS materials is as the reference resonat or element for a stable frequency source. A high Q superconducting res onator operated at low reduced temperature (T/T-c much less than 1) sh ould offer excellent frequency stability due to its low temperature co efficient of resonant frequency. HTS planar resonators appear to be pa rticularly promising since a reduced temperature of 0.1 may be readily achieved with a closed-cycle cryocooler. We report here microwave mea surements made on YBCO films grown by pulsed laser deposition (PLD), u sing both a Nb cavity and a parallel-plate resonator configuration, wi th particular emphasis on the variation of resonant frequency with tem perature. We compare the data with simple theoretical models and find evidence from the low temperature data fora low energy gap parameter D elta(0)=6meV. Some predictions of attainable frequency stability of pl anar resonator structures are also made.