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Confusion in HTS

  1. Mar 20, 2006 #1
    Hi,

    I've been reading a book recently about high-Tc superconductivity and I have some questions. They are really just questions about the definitions of various properties and variables...

    1) Definition of the pseudo-gap? (and for that matter the 'gap' too)

    2) The Knight shift?

    3) What exactly is a 'grain boundary'? Does this mean the whole bulk material is granular or just NS boundaries?

    Thanks,
    Natski
     
  2. jcsd
  3. Mar 20, 2006 #2

    ZapperZ

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    The pseudogap, as applied to HTS, is a gap in the single-particle energy spectrum that exists above Tc.

    In conventional superconductor, a gap forms below Tc in the energy spectrum. This gap corresponds to the strength of the coupling between 2 electrons that make up the Cooper pair. So to break up one, you need to supply that much energy. Above Tc when the material isn't in the superconducting state, no gap.

    In HTS, while there appears to be no gap in the overdopped regime, there clearly is a gap (often nothing more than a depression in the single-particle spectrum) above Tc for the optimally doped and underdoped cuprates. This is what has been called the pseudogap.

    This is an NMR question and not specifically on HTS. How much of NMR do you know?

    This is a materials question and also not specific to HTS. Grain boundary simply is the boundary between one single-crystal domain with another.

    Zz.
     
    Last edited: Mar 20, 2006
  4. Mar 20, 2006 #3
    Does the Spectral Frequency lines change in a Superconductor when going from room temperature to Super Cooled?

    I would assume that the cooper paired Electrons would change the band gap and cause a shift in the Spectral Frequency lines, wouldn't it?

    If so, is there any data that displays the differences in Spectral Frequencies between temperature dependancy states in a Superconductor compared to its non-Superconductive state? :bugeye:
     
  5. Mar 21, 2006 #4

    ZapperZ

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    What are "spectral frequency lines"?

    Zz.
     
  6. Mar 21, 2006 #5
    Hi Zz.

    Please forgive my lack of information when delivering my last question.

    dark lines (an absorption spectrum)

    I was wanting to know if the absorption spectra changed in a Superconductor when going into a Cooper Paired State compared to its non Cooper Paired State.

    _____________________________________
    Sincerely sits to down to listen to the Illuminated one.:bugeye:
     
    Last edited: Mar 21, 2006
  7. Mar 21, 2006 #6

    ZapperZ

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    You do know that "lines" are discrete absorption spectrum, where as "bands" are continuous. The "gap" that is in the single-particle spectrum is the absence of states in the ENERGY BAND.

    Secondly, you very seldom (I can't find any) see studies of "absorption" spectrum for a superconductor. Why? Because it's a metal (even a bad one), and within the relevant range, an EM radiation can only penetrate up to the skin depth of the material, which is even significantly less in the superconducting state. So this isn't a "prism" where light can be diffracted and looked at after it comes out of the medium. Practically all of optical conductivity experiments on HTS are done by looking at the reflected light and then reconstructing the transmitted portion via Kramers-Kronig transformation. You do not see any spectral "lines" here. You do however detect a range where there is a dip in the spectral response that corresponds to the energy gap.

    Zz.
     
  8. Mar 29, 2006 #7
    Thanks for answering my question Zz.
    Your the Greatest.

    Jerry:bugeye:
     
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