Magnetoresistance of p-GaAs/AlGaAs structures in the vicinity of   metal-insulator transition: Effect of superconducting leads
  Experimental and theoretical studies on transport in semiconductor samples with superconducting electrodes are reported. We focus on the samples close to metal-insulator transition. In metallic samples, a peak of negative magnetoresistance at fields lower than critical magnetic field of the leads was observed. This peak is attributed to restoration of a single-particle tunneling emerging with suppression of superconductivity. The experimental results allow us to estimate tunneling transparency of the boundary between superconductor and metal. In contrast, for the insulating samples no such a peak was observed. We explain this behavior as related to properties of transport through the contact between superconductor and hopping conductor. This effect can be used to discriminate between weak localization and strong localization regimes. 
N.V.Agrinskaya, V.I.Kozub, A.V.Chernyaev, D.V. Shamshur, A.A. Zuzin