ABSTRACT
If a normal metal N is deposited on top of a superconducting metal S, and if the electrical contact between the two is good, Cooper pairs can leak from S to N. This “proximity effect” is of comparatively long range:The thickness K − 1 of the leakage region on the N side is typically 103 Å (and can be made even larger if desired). This allows one to work with metallic films of rather large thickness, for which the thickness, the chemical composition, and the metallurgical state can be controlled with reasonable accuracy. (Compare, for instance, with the leakage of magnetic electrons from a ferromagnetic metal into a normal metal: Here the characteristic lengths are at most of order 1006100 Å, and the existence of a proximity effect has not yet been convincingly established.)
