Superconductivity in metal-semiconductor eutectic alloys

In an eutectic alloy obtained by melting the constituents, alternating domains of metal and semiconductor can exist in a well-defined microscopic array. The possibility of superconductivity arising from an interface interaction between the metal and semiconductor has been investigated. Superconductivity has been observed as a bulk property of some eutectic alloys (e.g., Al-Si and Al-Ge). Transition temperatures well in excess of those for the pure metal were found. The effect of rapid cooling the alloys from the liquid state on the microstructure and on the superconducting properties has been studied. It was found that a decrease in the characteristic domain sizes of the metal and semiconductor was accompanied by an increase of the superconducting transition temperature of the alloy. The results suggest that the enhancement of Tc depends on the Fermi energy of the metal. In metal-metal eutectic systems with comparable microstructure, no increase of Tc was observed. Several explanations of the experimental findings are considered. The exciton mechanism discussed by Ginzburg and by Allender, Bray, and Bardeen is considered as a possible means to account for the enhancements of the metal Tc's