The low-temperature magnetoresistance of Si/Nb superlattices

We have studied the correlation between localisation and superconductivity in two-dimensional thin films of amorphous Si/Nb. Si/Nb superlattice films, which exhibit superconducting transitions below 2 K, and a Si/Nb/Si sandwich film, which exhibits no superconducting transition down to 0.3 K, were fabricated in this experiment. In order to clarify their mesoscopic properties, we have measured the low-temperature magnetoresistance and analysed this using the transport parameters of weak localisation theory. The analysis suggests that the onset of superconductivity occurs once the superconducting coherence length becomes shorter than the inelastic scattering length, and we deduce that the onset of superconductivity in the disordered films is controlled by these characteristic length scales.