# Intuitive explanation for the existence of an energy gap in superconductors

In 2012 there was a nice answer explaining basic superconductivity. It ends with the sentence:

The trouble is you're now going to ask for an intuitive description of why the electron correlations open a gap in the energy spectrum, and I can't think of any way to give you such a description. Sorry :-(

Can anyone please follow up with an intuitive explanation of the energy gap in super conductors? In theory it can be derived from the BCS theory -- but this is not, what I would call intuitive ;)

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What do you mean more precisely with "energy gap" in SC? – Ignacio Vergara Kausel Apr 9 '15 at 8:54
Something like this: nature.com/nature/journal/v418/n6899/images/418733a-f1.2.jpg – bernd Apr 9 '15 at 9:04

The short, simple, and intuitive explanation is that in a superconductor state, electrons are paired (BCS case) because there is an effective interaction between them.

To destroy such a pair and produce free electrons you need to invest a minimum of energy, which is this energy gap $\Delta$. This produces an excitation (2 free electrons), remember that SC is the ground state of the system.

This is not so different than band gap excitations in semiconductors, where you need a minimum of energy to go from the valence to conduction band.

Hope it helps

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