Electron transport and magnetic penetration depth in niobium-silicon multilayers

Thin niobium-silicon multilayers have been sputtered with niobium thicknesses less than the coherence length and silicon thicknesses that allow tunneling between layers. The multilayer structure has been confirmed by X-ray diffraction, and the films have been electrically characterized with respect to T/sub c/ and J/sub c/. For constant Nb thickness, both T/sub c/ and J/sub c/ increase with decreasing Si thickness, indicating increased coupling between the Nb layers. When a multilayer forms the barrier in a tunnel structure, the resulting I(V) characteristic resembles that for a series of single-barrier junctions, and further evidence of Nb interlayer coupling is observed. These multilayers have also been incorporated as the base in several tunnel structures in order to measure the multilayer penetration depth via the magnetic field dependence of I/sub c/. Preliminary results indicate that the theoretically predicted enhancement of penetration depth in a multilayer does occur.<>