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Phonon/momentum/rest mass

  1. May 14, 2009 #1
    do phonons have (significant) momentum? do they have rest mass?
     
  2. jcsd
  3. May 14, 2009 #2

    malawi_glenn

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    define "significant".

    No photons have no rest mass, they are massless.
     
  4. May 14, 2009 #3
    phonons. not photons.

    significant as in not trivial. (light carries a trivial amount of momentum)
     
  5. May 14, 2009 #4

    malawi_glenn

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    Last edited by a moderator: Apr 24, 2017
  6. May 14, 2009 #5
    thank you. I'll have to digest that for a while. its mostly over my head. but it answers my question.

    do phonons and antiphonons exist in equal numbers in ordinary materials?
     
  7. May 14, 2009 #6

    malawi_glenn

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    define antiphonon, you mean a phonon that has wave number -k is the antiphonon to phonon with wave number k???

    maybe you just should pick up a textbook on solid state physics, e.g Kitell?
     
  8. May 14, 2009 #7
    Acoustic phonons do not have mass; that's guaranteed by them being the Goldstone bosons of broken symmetries. Compared with photons, they have much lower speed, so for the same energy, they have vastly greater momentum. In semiconductors, electronic transitions via pure photon processes are called "vertical" because the photon momentum is negligible, whilst phonon processes are called "horizontal" because they're energies are almost negligible.
     
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