Proximity coupling effect in NbTi fine-multifilamentary superconducting composites

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Abstract
In order to shed light on the proximity effect in fine multifilamentary wires with NbTi filaments, measurements of magnetic susceptibility were conducted at 4.2 K for various values of electrical resistivity of the matrix between filaments, of the distances between filaments, and of the applied magnetic field strength. It was confirmed experimentally that in weak fields (10 mT or less), the critical distance for the occurrence of proximity coupling was several multiples of the characteristic leak distance of Cooper pairs in normally conductive metal, and that when the distances between filaments were large, the breakdown field decreased exponentially, irrespective of the electrical resistivity of the matrix.