Measurements of contact resistance between normal and superconducting metals

The contact resistance between crossed wires of Pb and Sn, Pb and Cu, Sn and In separated by their natural oxide layers has been measured at constant temperatures as a function of current direction and magnitude. Plots of these measurements in the case of a normal and a superconducting element show the resistance at low currents to be constant and to increase suddenly above a critical current. The low current resistance generally decreased with decreasing temperature. Calculation of the radius of the current-bearing area gives radii of atomic dimensions and shows that in some cases part of the barrier resistance disappears. Furthermore, four contacts showed an immeasurably small resistance at a temperature where only one of the contact members was superconducting. These measurements and earlier ones by others suggest a schematic representation of the resistance as a function of current and temperature. No significant rectification between normal conductors and superconductors was observed.