Superconductivity in rapidly quenched metallic systems with nano scale structure

Abstract

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 ξ₀≥d≥ d_min, where ξ₀ is the superconducting zero temperature coherence length and dmin is the minimum particle size that supports superconductivity. The onset of superconductivity generally starts in samples with d~ξ₀ and progressively other grains with d≤ ξ₀ 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~1.33 times the T_c of Al. But in Al-Pb and Zn-Pb, the zero resistivity state is obtained at T~4 and 5 times the T_c of Al and Zn with only 10-15 wt % Pb, respectively.