Study of closely spaced YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta// Josephson junction pairs

Using electron beam lithography and ion damage, high quality YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta// superconductor-normal metal-superconductor in-plane Josephson junction pairs have been fabricated. These junctions operate at temperatures between 60 and 85 K and have spacing ranging between 150 nm and 800 nm. Central electrodes connecting to the area between the two junctions were made, allowing for simultaneous measurements of the individual junctions as well as the series. Josephson junction pairs with 150 nm spacing were found to have extraordinary properties under microwave radiation with different power. At low power the structure functioned as two independent Josephson junctions in series, while at high power it behaved as one single Josephson junction. A possible origin of this behavior could be that the applied microwave radiation induces weak link behavior in the YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta// between the two junctions.