Direct study of the proximity effect in the normal layer inside of the stacked SINIS device

We have observed a striking anisotropy in the electrical transport of layered multiterminal SINIS structures [where S, I, and N denote a superconductor (Nb), an insulator (AlOx), and a normal metal (Al), respectively]. We find that the lateral conductivity of the N layer is dissipative, but a superconducting current can flow normal to the structure, suggesting a direct Josephson coupling between the external S electrodes. A small coherent contribution to the lateral conductivity of the N layer is observed near zero voltage.