Properties of the N layer inside of a SINIS sandwich-type Josephson junction*

We report characteristics of a multi-terminal SINIS device which has electrical leads connected to the middle N layer; here S, I, and N denote a superconductor (Nb), an insulator (AlO$_{x})$, and a normal metal (Al) respectively. Specifically, we studied properties of the middle (10-20 nm thick) N layer in dependence of Josephson current passing through all layers and on an injection current passing through one of the individual (NIS) junctions. The unperturbed I-V curve of the N film displays a small phase-coherent current near zero voltage, which can be suppressed by a very weak magnetic field (applied in parallel to the layers). In the last case, the state of the N film may be regarded as normal; at the same time, a sufficiently high supercurrent can flow between the S electrodes. An injection current (lower than the Josephson current) from one junction induces additional phase-coherent contribution to the I-V curve. We consider possible explanation of the observed behavior.