Superconductive tunneling in molybdenum

The technique of electron tunneling through a Schottky barrier which is created by a pointed single crystal of degenerate gallium arsenide in mechanical contact with a bulk molybdenum sample was used to obtain the superconducting energy gap and its temperature dependence for pure molybdenum. Some indication of phonon spectrum for molybdenum as well as gallium arsenide was observed from the tunneling characteristics. The transition temperatures of molybdenum and its very dilute alloys with iron concentrations up to 80 ppM were measured. There is no measurable superconducting energy gap for alloys with 27.5 ppM or more of iron in molybdenum while the transition temperature is nonzero. All these measurements were carried out in a 3He-4He dilution refrigerator which can reach to a temperature down to the millikelvin range. The spin-flip lifetimes of electrons due to magnetic impurities in alloys are calculated from both superconducting transition temperature results and resistivity measurements. A large zero-bias anomaly has been observed in the gallium arsenide/molybdenum junctions. The anomaly corresponds to a resistance peak centered at zero bias. The junction resistance at zero-bias is a strong function of temperature. When the temperature was lowered below the transition temperature of molybdenum, the superconducting energy gap of molybdenum was observed, which indicated that the mechanism of current flow is by electron tunneling. (Diss. Abstr. Int., B)