Proximity Effect in a Normal Metal

When a superconductor is attached to a normal metal, a Cooper pair penetrates into the normal metal. As a result, the normal metal possesses superconducting-like properties such as screening of magnetic fields and decreasing its electric resistance. Such phenomenon is called proximity effect and has been a central issue in the physics of superconductivity. In order to describe the proximity effect correctly, we need to use Green’s function technique. In this chapter, however, we will try to explain the essence of the proximity effect phenomenologically by applying the physical picture of the Andreev reflection.