7. Superconductivity - University of Liverpool

It has an energy 2E F − ∆, where ∆ is about 10 −4 E F . If two
electrons start with energy E F , this means that ∆ is the
binding energy. If ∆ is so much smaller, why do the electrons
not escape.
Physically, if a electron just escape, its wavefunction must
change to that of a free particle, i.e. a sine function, with
energy E F − ∆/2. However, this is just below E F , where the
states are fully occupied. This is not allowed by the exclusion
principle.
Superconductivity 62