Cooper Pairing Revisited

We recall the fundamental fact that Cooper pairs defined without ignoring two- hole pairs along with two-particle ones leads to a purely imaginary pair energy when the problem is based on the ideal Fermi gas sea. However, bound finite- lifetime pairs are recovered when it is based on the BCS ground-state Fermi sea. Their excitation energy is gapped at zero total momenta and then rises linearly in either 2D or 3D, making them similar to 3D plasmons which however rise quadratically.