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Phonon condensation

  1. Nov 9, 2007 #1
    Hi , i need some scientific source (book, article etc.) on phonon condensation in solids. Google scholar seems to fail in this topic. Can anyone advice me some source ?
  2. jcsd
  3. Nov 12, 2007 #2
  4. Dec 1, 2007 #3
    I can not understand what phonon condensation means

    Atoms can condense to a single wavefunction because they are conserved, but phonon and photon are not conserved!

    If you lower the temperature of a solid to zero, the number of phonons decrease monotonically and vanishes identically at zero temperature, how can there be a phonon condensate?
  5. Dec 1, 2007 #4


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    The number of atoms in the condensate is itself not conserved. Besides, at a given temperature isn't the total phonon density conserved too? In any case, I'm not aware of the need for total particle number conservation.

    This does not preclude the possibility of a phonon condensate at T>0. Keep in mind also, that the common method of cooling alkali atoms in traps necessarily results in the total particle number decreasing monotonically with temperature, and vanishing at T=0.

    Also, in addition to all this, you need to keep in mind that most atomic BECs are only quasi-equilibrium systems (conservation rules apply over not-too-long time scales).
    Last edited: Dec 1, 2007
  6. Dec 2, 2007 #5
    The atoms in the condensate is not conserved, but the total number of atoms is conserved. BEC occurs because the excitation levels can not accomodate the whole of the atoms, so the remaining atoms have to reside in the ground state. In this argument, it is quite clear that atom conservation is necessary for the occurence of BEC.

    but in priciple, we can avoid the atom-loss and keep the number of atoms a constant.
  7. Dec 2, 2007 #6
    In fact, the paper posted above talks about non-equilibrium state of phonons

    My view-point is that, there is no phonon condensate at equilibrium
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