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Help, Density of States

  1. Feb 25, 2006 #1
    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
  2. jcsd
  3. Feb 25, 2006 #2


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    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.

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