Jh. Clark et al., TEMPERATURE-DEPENDENCE OF SURFACE IMPEDANCE OF PULSED-LASER-DEPOSITEDYBCO FILMS, IEEE transactions on applied superconductivity, 5(2), 1995, pp. 2555-2558
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.