ABSTRACT
The fundamental ideal behind all of a superconductor’s unique properties is that superconductivity is a
quantum mechanical phenomenon on a macroscopic scale created when the motions of individual electrons
are correlated. According to the theory developed by John Bardeen, Leon Cooper, and Robert Schrieffer (BCS
theory), this correlation takes place when two electrons couple to form a Cooper pair. For our purposes, we
may therefore consider the electrical charge carriers in a superconductor to be Cooper pairs (or more
colloquially, superelectrons) with a mass m* and charge q* twice those of normal electrons. The average
distance between the two electrons in a Cooper pair is known as the coherence length, x. Both the coherence
length and the binding energy of two electrons in a Cooper pair, 2D, depend upon the particular
superconducting material. Typically, the coherence length is many times larger than the interatomic spacing of
a solid, and so we should not think of Cooper pairs as tightly bound electron molecules. Instead, there are
many other electrons between those of a specific Cooper pair allowing for the paired electrons to change
partners on a time scale of h/(2D), where h is Planck’s constant.