Understanding the Density of States Diagram in Insulators and Superconductors

[nicola_gao]

The Density of States diagram gives gaps sometime. As I know, if the band is filled up to the gap, then the material is an insulator.
However, it seems to me, that superconductors also open a gap in their density of states diagram, as BCS theory says.

If my understanding is correct, I am a little confused here, so how can you tell the difference between an insulator and an superconductor?

Thanks a lot for whom could give me some help

 

[ZapperZ]

The Density of States diagram gives gaps sometime. As I know, if the band is filled up to the gap, then the material is an insulator.
However, it seems to me, that superconductors also open a gap in their density of states diagram, as BCS theory says.

If my understanding is correct, I am a little confused here, so how can you tell the difference between an insulator and an superconductor?

Thanks a lot for whom could give me some help

One type of gap is not the same as other gap.

The "gap" in insulators and semiconductors are BAND GAPS. The gap in a superconductor is not a band gap - it is the gap in the single particle spectrum. This is the energy that you need to break up a Cooper pair. This is not a band gap.

Furthermore, the gap size in an insulator/semiconductor does not change in size with temperature other than thermal broadening. The gap size in a superconductor does change with temperature, getting smaller with increasing temperature. In addition, the conductivity in a superconductor is due to the supercurrent, i.e. a 2-particle state, rather than a single-particle state.

So not all gaps are the same.

Zz.