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Gibbs Free Energy in Superconductors

  1. Mar 3, 2015 #1
    When reading some material concerning Ginzburg-Landau theory of superconductors, I got the following sentence:

    The appropriate thermodynamic potential for describing a superconductor in an applied magnetic field is the Gibbs free energy ##G## (natural variable ##H##) and not the Helmholtz free energy ##F## (natural variable ##B##).

    I don't understand the sentence. In gas, Gibbs free energy is minimal in constant temperature and pressure. Does this sentence mean that in superconductors Gibbs free energy is minimal in constant ##T## and ##H##? I can't make sense out of it.
     
  2. jcsd
  3. Mar 5, 2015 #2

    DrDu

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    L&L discuss quite extensively their peferred thermodynamic variables in the case of magnetic fields in previous chapters.
     
  4. Mar 6, 2015 #3
    You mean Landau and Lifshitz‘s textbook?
     
  5. Mar 6, 2015 #4

    DrDu

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    Sorry, yes, I had erroneously in mind that you had mentioned Landau & Lifshitz. The relevant pair of variables in case of magnetism is not p and V but B and H and you can analogously define energies and enthalpies with different natural variables.
    I think that thermodynamics in the presence of fields is quite a non-trivial matter. Much of the distiction whether B or H are to be preferred depend on the measurement you have in mind and on the chosen separation into system and surrounding, especially, which part of the field belongs where.
     
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