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 m ; length 3–15 m ; width 10–100 m. Josephson behavior has been observed in bridges up to 20 m 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.Supported by a grant of the Deutsche Forschungsgemeinschaft.