Magnetoresistance of Si/Nb/Si Trilayers

We study the superconductor-insulator transition in Si/Nb/Si trilayers, in which the thickness of Si is fixed at 10 nm, and the nominal thickness of Nb changes in the range between d = 20 nm down to d = 0.3 nm. The transmission electron microscopy indicates the formation of the mixed Nb-Si layer for small d. Both the thickness-induced, and the magnetic-field induced superconductor-insulator transition is observed. The crossing point of the isotherms at the critical field $B_{c}$ decreases with decreasing d, and it is T-independent at temperatures below 300 mK. At larger fields the weak peak in magnetoresistance appears in some of the films.