Superconducting Transition of Quench-Condensed Ultrathin Films

The condition of the onset of superconductivity in highly homogeneous ultrathin Bi and Pb films has been investigated by measuring the temperature dependence of the sheet resistance R □ . The experimental results suggest that highly homogeneous metal films with R □ lower than ∼6 k Ω could be superconducting, while those with R □ greater than ∼6 k Ω are insulating at zero temperature, in agreement with the condition of the onset of global superconductivity in granular films. The superconducting transition temperature T c shows a remarkable decrease with increasing the normal-state sheet resistance, unlike the results of granular films.