INVESTIGATION OF DC JOSEPHSON CURRENT DISTRIBUTION IN DOUBLE-BARRIER 3-TERMINAL DEVICES WITH A THIN MIDDLE SUPERCONDUCTING LAYER

Nb/Al-Al0(x)-Nb/Al-Al0(x)-Nb double-barrier three-terminal Josephson d evices with a thin middle Mb/Al bilayer, which have potential for use as switching and amplifying elements in superconducting electronics, h ave been investigated in the stationary state by means of low-temperat ure scanning electron microscopy. For the devices with lateral sizes c omparable with the effective Josephson penetration depth, we observed nearly homogeneous current distribution over the region common to the top and bottom junctions when the devices were biased across both the barriers in the absence of an external magnetic field. When the two ju nctions are biased separately, the current is concentrated at the junc tion edges in accordance with the behavior characteristic of distribut ed junctions. In an applied magnetic field, the vortex structure is co nfined to the area shared by both junctions when the device is biased as a whole. The experiment gives an indication that in the stationary state the spatial phase difference distribution of the two junctions c oincides in the shared region at least in some interval of the externa l magnetic field. (C) 1996 American Institute of Physics.