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What defines a polaron?

  1. Jun 23, 2015 #1
    Is there an easy-to-articulate difference between a polaron and an electron exhibiting electron-phonon coupling? Until yesterday, I had been under the impression that the difference between the two phenomena was related to the strength of the coupling. However, I looked up "polaron" on Wikipedia, and the lede paragraph left me confused. The definition listed by Ashcroft & Mermin is similarly vague (see p. 626).

    If there is no meaningful difference between the two concepts, it seems to me that electronic quasiparticles ought to more properly be called polarons in in basically every solid ever, since it is hard to imagine a crystal where the electronic forces between electrons and the ions have no effect.
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  3. Jun 24, 2015 #2

    Simon Bridge

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    Polarons are a subset of "carrier-phonon coupling" (not just electrons, any charge carrier in a solid) and is defined by the mathematical description that comes in the polaron models - so it is not surprising you are having trouble coming up with a non-technical, word-based, description that is helpful. Your question, basically, is: when does regular charge-phonon coupling become a polaron ... and the answer is that it happens when the polaron model is more useful than other models for describing the result. The polaron is not a class of physcal object so much as the label given to a way of modelling properties in solid state physics. The boundaries between different models field of use is fractal.

  4. Jun 24, 2015 #3


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    I am mostly with you here. But take in mind that the concept of a quasi-particle implies that it has a considerable lifetime (or, stated, differently, that the imaginary part of its energy is small). This is usually only the case for particles sufficiently near the Fermi energy.
  5. Jun 25, 2015 #4
    Thanks to you both. These comments are helpful.
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