The Nature of the Cooper Pair - University of Liverpool

Let us see what the wavefunction looks like.
Ψ =
�ω
�D
0
1
ε + ∆
sin kr
It is a function of r only, so it is spherically symmetric. It is a
sum of many sine functions. The coefficient decreases with
energy. When the energy ε goes from 0 to ∆, the coefficient
decreases from 1/∆ to 1/(2∆).
So we may suppose that the terms are only significant in the
energy range from 0 to ∆. As energy changes, k changes.
When r is large enough, sin kr starts to go out of phase for
different wavevectors k.
Superconductivity 21