I have here a copy of the original paper by Bardeen, Cooper, and Schrieffer 'Physical Review, Vol 108 Num 5 December 1, 1957' The abstract started with the following excerpt
"A theory of superconductivity is presented, based on the fact that the interaction between electrons resulting from virtual exchange of phonons is attractive when the energy difference between the electrons states involved is less than the phonon energy,
. ...."
the phonons, they are talking about are the bosonic states of fermionic electrons. Phonons are the quanta of sound waves and the speed sound is dependent on the temperature of the medium. Can there be a connection between phonons and photons and their speeds?