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Matter waves - Real or Hypothetical?

  1. Sep 25, 2011 #1
    Hi my expert friends,

    I'm confused with these seemingly two contradictory statements:

    1- Phonons are the quantized quasi-particles of the normal modes of lattice vibrations and we have Longitudinal (LA) and Transverse Acoustical (TA) Phonons and Longitudinal (LO) and Transverse Optical (TO) Phonons

    2- de Broglie Matter waves are neither transverse nor longitudinal. They do not represent any physical oscillations and obviously wave solution for Ψ cannot have a polarization associated with it.

    Can anyone explain, clearly, the associated phonons waves are those lattice normal modes of viberation (which can be either transverse or longitudinal) or they are hypothetical waves (which do not represent any real physical oscillations)?

    Thank you in advance
  2. jcsd
  3. Sep 25, 2011 #2


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    Phonon waves are NOT "de Broglie Matter waves"! Normal modes of lattice vibrations is not the same as particle waves due to quantum particles moving with a particular momentum.

  4. Sep 25, 2011 #3

    Vanadium 50

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    Why do you think those two statements have anything to do with each other?
  5. Sep 25, 2011 #4
    Let me clarify what I meant,
    Suppose that I have a purely sinusoidal traveling transverse wave. I want to know can I assign a quasi-particle to it? If yes, the associated wave of this quasi-particle isn't transverse?

    ZapperZ, you are right. normal modes are stationary. but my original question still is unanswered, are phonon waves hypothetical or they have any physical representation in the lattice?
  6. Sep 25, 2011 #5
    unsure what you mean by "physical representation" but such excitations sure do have effects on the state of lattice structures....

    Do you consider "lattice vibrations" a "physical representation"??

    good discussion here: ...
  7. Sep 25, 2011 #6
    nahira: I just noticed the wording in the second part of your first post:

    sounds like you DO consider lattice vibrations a "physcial representation"....

    so I may be missing your real intent...
  8. Sep 25, 2011 #7


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    This is rather puzzling. You cannot assign a "particle" to anything you like, such as a "sinusoidal" wave. A "quasiparticle" isn't something that anyone can invent! There is a very strict rule on what a quasiparticle is, per Landau's Fermi Liquid theory!

    Phonons are as physical as any collective excitation.

  9. Sep 25, 2011 #8

    Thanks to you my brother.
    I've got the point. :smile:
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