The Nature of the Cooper Pair - University of Liverpool

So, as in superfluid helium-4, we may expect phonons and
rotons, and that the critical velocity be determined by the
minimum roton excitation.
If we think of the rotation as a rotation of two Cooper pairs
about each other, we can relate the roton excitation to the
minimum rotational energy. The rotational energy is quantised
and the minimum is given by 2� 2 /meD 2 .
If we put in the numbers, we would find that this is much larger
than ∆, the binding energy for the Cooper pair. The Cooper
pair would break before any roton gets excited.
As long as there is not enough energy to break the Cooper
pairs, the Cooper pair condensate flows with zero resistance.
This condesate is also called the BCS superfluid. This explains
why a superconductor has zero resistance.
Superconductivity 30