Josephson effect in indium bridges with large dimensions

We report experiments searching for Josephson behavior in indium bridges with dimensions in the following range : thickness 2–3 Μm ; length 3–15 Μm ; width 10–100 Μm. Josephson behavior has been observed in bridges up to 20 Μm wide prepared by a single-step evaporation procedure and photolithography. In this case the V-I characteristics, including the rf-induced step structure, can be well described by the RSJ model if the amplitude of the applied rf current exceeds a distinct value. These results and in particular the magnitude and temperature dependence of the normal resistance of the Josephson element can be explained by the formation of an extended, “two-dimensional” phase slip center. Indium bridges prepared by a multiple-step evaporation method often show complicated behavior, the Josephson effect being localized somewhere within a contamination layer separating the underlay films from the overlay film representing the bridge. Such multiple-step evaporation procedures should therefore be avoided.