Abstract
We have fabricated trilayered sandwiches consisting of superconducting electrodes made of MoRe alloy with a critical temperature of about 10 K and a silicon interlayer of thicknesses up to 20 nm doped by tungsten with atomic concentrations up to 10 at%. For concentrations below 5 at%, measurements of transport characteristics have revealed the presence of charging energy in ultra-small dopant granules (the Coulomb-blockade effect) without any supercurrent through the junction. Unexpectedly, a persistent current at zero voltage bias has exposed itself at higher W concentrations and even for the thickest W:Si layers. Microwave-radiation experiments have proven that in this case we are dealing with a Josephson current. The observation is explained as the fingerprint of ‘open’ channels in the charge transmission due to resonance-percolating trajectories inside the strongly inhomogeneous silicon interlayer with metallic nanoclusters. We have calculated the ratio of super- and excess currents using a universal distribution function for randomly arranged localized states and found good agreement with our experimental data without any adjustable parameters. The novel functionalities due to the disorder in doped semiconducting films make it possible to fabricate trilayered junctions with enhanced conductance properties and, at the same time, with well separated metallic electrodes.
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