Can anyone please clarify my confusion?
Why does a superconducting state conducts electricity even if it has an energy gap?
The difference between metals and insulators is that there is a gap at the Fermi energy so electrons cannot be excited (i.e. the band is full). In superconductor, we have fully occupied lower band and a gap $2*\Delta$ and yet it still conducts electricity (with zero resistance of course).
I guess that these two things are not quite related where one concerns the state of single electrons and the other concerns pairs of electrons.
Thank you in advance!