High frequency properties of YBCO bridges fabricated by MOCVD

Abstract

The high-frequency properties of YBCO (YBa/sub 2/Cu/sub 3/O/sub 7- delta /) bridges at 4.2 K and 77 K are discussed. The YBCO films were prepared by MOCVD. For small bridges with a width (w) of about 1 mu m and thickness (t) of less than 0.5 mu m, the constant voltage steps at integral multiples of Phi /sub 0/fr-20 mu V were observed up to 1 mV, which is much higher than the I/sub c/R/sub N/ (<0.13 mV) product of these bridges at 77 K. The magnitudes of the current steps as functions of the RF current at 4.2 K and 77 K were in quantitative agreement with the theoretical results based on the RSJ (resistively shunted junction) model. The DC SQUIDs with these small bridges had a good response to external magnetic flux, resulting in a sinusoidal current-phase relation. On the other hand, for large bridges of w>5 mu m and t=1 mu m, the chaotic I-V characteristic was observed, and the shape of chaotic I-V curve was in qualitative agreement with the simulating results based on an RSCJ model.