Superconductivity in Metal-Semiconductor Eutectic Alloys.

The superconductivity of several metal-semiconductor simple eutectic alloys containing Ge or Si, and one of the metals Al, Be, In, Pb, Sn, or Tl was investigated. The liquid-quenching technique was used to reduce the characteristic scale of the microstructure in the alloys. It was found in some cases (notably Al-base alloys) that the superconducting transition temperature of the metallic phase was significantly enhanced as a result of liquid-quenching. The characteristic scale of the microstructure was found to be of the order of several hundred angstroms in alloys showing the greatest enhancement effect. The results are discussed in terms of recent theoretical models that predict enhancement of superconductivity due to electronic interactions at a metal-semiconductor interface. The results are also analyzed in terms of the McMillan theory of superconductivity in which the enhancement effect is attributed to a reduction in the characteristic phonon frequencies of the metal.