MODIFICATION OF NORMAL-METAL TRANSPORT BY THE SUPERCONDUCTING PROXIMITY EFFECT

When a normal (N) metal makes intimate contact with a superconductor ( S), the density of states in the normal metal is modified by the proxi mity effect. As a consequence, if a point contact is made with the nor mal metal the resulting tunnel conductance, G, is a function of the di stance, x, from the N-S interface. We show that, for all x, G possesse s a minimum at zero voltage and at finite voltage, G equals that of th e structure without superconductivity present. The conductance is inde pendent of the magnitude of the super conducting order parameter but d epends upon the amount of normal scattering at the N-S interface.