Low-frequency noise of YBCO/Au junctions

We have fabricated ex-situ c-axis YBCO/Au junctions with low contact resistivities. These devices exhibit large low-frequency resistance fluctuations. At room temperature the junction noise spectrum is 1/f like. At liquid nitrogen temperature (77 K) and lower, the noise spectrum depends sensitively on the bias current, with certain bias levels producing clear two-level fluctuation behavior. The normalized resistance noise for these junctions at temperatures below 77 K has an average value of 2 to 3/spl times/10/sup -5/(Hz)/sup -1/2/. We discuss practical issues related to junction noise properties.