SUPERCONDUCTIVITY IN RAPIDLY QUENCHED METALLIC SYSTEMS WITH NANOSCALE STRUCTURE

Nanocomposites of Al-In, Al-Pb, and Zn-Pb have been prepared and characterized using rapid quenching techniques and the nature of superconducting transitions in them has been studied by resistivity measurements. The precipitated second phases (In and Pb) have particle sizes (d) of a few tens of nanometers such that xi0 > d > d(min), where xi0 is the superconducting zero temperature coherence length and d(min) is the minimum particle size that supports superconductivity. The onset of superconductivity generally starts in samples with d is similar to xi0 and progressively other grains with d < xi0 become superconducting. We suggest that the proximity effect of the matrix plays a significant role. In an Al-In system, even with 40 wt.% In, the zero resistivity state is obtained at T is similar to 1.33 times the T(c) of Al. But in Al-Pb and Zn-Pb, the zero resistivity state is obtained at T is similar to 4 and 5 times the T(c) of Al and Zn with only 10(-15) wt % Pb, respectively.