ANOMALOUS ZERO-MAGNETIC-FIELD DISSIPATION ACROSS YBCO THIN-FILM MICROBRIDGES IN LAYERED YBCO-BAF2-SN DEVICES AT LOW-TEMPERATURES

We have studied the zero-magnetic field current-voltage characteristic s of a YBCO thin-film microbridge (T-c= 85 K), which is separated from a Sn film by a 290 nm thick insulating BaF2 layer. At 4.2 K, with the Sn normal and the YBCO superconducting, we find the voltage across th e YBCO is zero (within 20 nV) up to the critical current. As the tempe rature is lowered below the T-c of the Sn a small voltage develops acr oss the YBCO at currents well below the critical current, indicating t he onset of a new dissipation mechanism related to the presence of the superconducting Sn layer. The results are not consistent with convent ional dissipation mechanisms. One possible explanation is based on the onset of a cut-rent-driven plasma instability between the ''collision less plasmas'' of the Sn and YBCO layers.