Superconductivity and normal electrical conductivity of amorphous lead films nucleated with molybdenum

Lead films vapor quenched onto nucleating monolayers of Mo or W exhibit strong lattice disorder and can be considered to be amorphous. The amorphous-to-crystalline transformation temperatureT_tr is indicated by a sharp drop of the electrical resistivity in the course of annealing.T_tr is found to be proportional tod^–2 for Pb thicknessd smaller than 30 nm. The superconducting transition temperatureT_c is by 0.6 to 1 K smaller in the amorphous state than after crystallization. In both states,T_c is proportional tod^–1. Prenucleation with about half a monolayer of Mo leads to quite the sameT_c depression as observed earlier by Strongin et al. on Pb films vapor quenched onto predeposited films of SiO, Ge or Al₂O₃. For comparison, experiments have been carried out with 2.5 nm Ge predeposits. As with Mo prenucleation, a well defined transformation temperatureT_tr of about the same value has been observed.T_c of bulk amorphous Pb can be extrapolated to be about 6.6 K.