ABSTRACT
It has been known since the 1960s (De Gennes and Guyon 1963) that charge carriers emitted from a superconductor can propagate in a non-superconducting medium, provided that the electron wave functions of the two electrons originating from the superconductor (the so-called Cooper pairs) keep their correlation during their di˜usion outside the superconductor. ›is process requires the absence of defects in the propagating medium that break timereversal symmetry, such as magnetic impurities. ›ese correlated electrons form an evanescent state that “bleeds” from the superconductors into the non-superconducting electrode on mesoscopic distances. ›e physics of these evanescent states, known as the “superconducting proximity e˜ect” depends on many parameters (the coherence length of the superconductor, the contact barrier at the interface, the temperature, the electron di˜usion length, etc.).
