Are phonon's actually a real particle, or is it a trick of QM?

[RHoisser]

Hi, a brief question from a confused undergrad, I'm about to start a section of a QM course that deals with the QM nature of condensed matter and think I should get a good idea on this before I start it.

I fully understand the wave-particle duality of photon's and electrons and the like, but I don't see how this works with phonon's.

From my rather basic understanding (all from before I learned enough about QM to understand it), a phonon is the localised vibration of atoms through a solid that allows sound to occur. So this is most definitely a wave-like property of a phonon.

But if it then follows from QM that this phonon must also have a particle-like property, what does this actually represent? Can a phonon have momentum?

Or do we get around this issue by calling it a "wave packet", which to me is like a really small bit of a wave moving like a particle?

Are these questions even worth asking, or it is just a case of "thats Quantum Mechanics"?

Cheers all

 

[ZapperZ]

Phonons are quantized lattice vibrations, which means that they represents the "normal modes" that are available in such a system.

http://www.physics.udel.edu/~bnikolic/teaching/phys624/PDF/phonon_wave_function.pdf

In particular, read the discussion on page 234.

Zz.

 

[A. Neumaier]

Hi, a brief question from a confused undergrad, I'm about to start a section of a QM course that deals with the QM nature of condensed matter and think I should get a good idea on this before I start it.

I fully understand the wave-particle duality of photon's and electrons and the like, but I don't see how this works with phonon's.

From my rather basic understanding (all from before I learned enough about QM to understand it), a phonon is the localised vibration of atoms through a solid that allows sound to occur. So this is most definitely a wave-like property of a phonon.

But if it then follows from QM that this phonon must also have a particle-like property, what does this actually represent? Can a phonon have momentum?

The only particle-like property (which is enough to call phonons ''quasi-particles'') is that one can associate with then creation and annihilation operators, and has exactly the same computational setting as one has in the quantum field theory of elementary particles.

 

[RHoisser]

Thanks for your replies A.Neumaier and ZZ, both very enlightening.

Now the only trouble I have is with the Fourier transforms to go from real space to reciprocal space, but that's going to be coming up in the lectures, so I shall wait and see if I can learn it that way.

Thanks again,

Richard