Physical question about Phonons

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Summary:

If I hit some material/give any energy to it, are phonons created?

Main Question or Discussion Point

Hi,

I have a question regarding Phonons and daily experience:

Let's say I have a table and I hit it, does it mean Phonons were created where I've hit on the table?

Meaning: By hitting the table, I'm giving energy to it, this energy goes to the motion of the table atoms, and this motion of the atoms is translated to Phonon motion ( so I've created Phonons )?

Another question: Phonons represent collective and ordered motion of atoms , meaning - Phonons represent normal modes. Therefore, if the motion of the table atoms is looking random after I've hit the table, then this just means that I've created Phonons with various normal modes, and the superposition of these normal modes gives me the random-looking motion of the table atoms. Am I correct?

Thanks in advance.
 

Answers and Replies

  • #2
vanhees71
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Phonons are the quasiparticles referring to the quantized collective vibrations of your body. Each mode is equivalent to an harmonic oscillator, which is the most simple system to be quantized. If you hit your table sound-waves travel through it, and that's why the quanta of these vibrational modes are calle "phonon", which you could roughly translate as "sound particle", but you must not think of phonons as pointlike localized particles. As this example shows it's rather a collective excitation of your table. The macroscopic sound wave also is of course not an excitation of a few phonons (i.e., a Fock state) but rather a coherent state. Which is a specific superposition with an indetermined number of phonons. So in some sense you can say you have "created phonons" but in a very specific sense.
 
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  • #3
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The Phonons i'm creating by hitting the table are acoustic, optical or both? , generally how can I choose for example to arouse only one specific type of phonon?

Also, is it more precise to say that by hitting the table - I am 'exciting' Phonons rather than 'creating' them?
 

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