How a phonon gain momentum?

In summary, Kittel's Introduction to Solid State Physics states that the phonons would gain some extra momentum when heated up, while the thermal conductivity explains how this extra momentum is transferred to the material.
  • #1
atib0539
2
0
Hi guys, I'm reading solid state physics, I have some doubts about phonons.

Here is the question, if we heated up a material, based on the the thermal equilibrium of occupancy of phonons given in Kittel's Introduction to Solid State Physics,

<n> = 1/(e^(\hbar\omega/kBT)-1)

so as T increases, we would excited some extra phonons. But in Introduction to Phonons and Electrons p.124, its states that the phonons would gain some extra momentum when heated up

"Consider a long rod in thermal equilibrium. The net phonon momentum is zero. Now, if we give a push to all the phonons at one end by applying a heat pulse, every phonon gains an extra momentum of equal amount along the direction of the rod. The net momentum is no longer zero but biased with a constant value, which gives rise to a current density of phonons..."

The question is, the excess energy absorbed by the material is to increase the number of phonons without increase the energy of phonons, or to increase the energy of phonons without increase the phonon number? I'm wondering which case is true or they're just using different models, or a combination of both?
 
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  • #2
atib0539 said:
But some articles states that the phonons would gain some extra momentum when the material is heated up when they explaining the thermal conductivity.

Whenever you have something like this, it is the policy of this forum that you cite the source. It is a good practice for when you have to write and publish a paper. Give us the exact citation as if you're writing a paper for publication.

Zz.
 
  • #3
ZapperZ said:
Whenever you have something like this, it is the policy of this forum that you cite the source. It is a good practice for when you have to write and publish a paper. Give us the exact citation as if you're writing a paper for publication.

Zz.

Thanks for the advice. :-)
 

1. What is a phonon?

A phonon is a type of quasiparticle that describes the collective vibration of atoms in a solid material. It is a unit of energy that carries momentum and is responsible for conveying heat and sound in a material.

2. How does a phonon gain momentum?

A phonon gains momentum through interactions with other phonons or with defects in the material's crystal lattice. These interactions can cause the phonon to scatter and change direction, resulting in a net gain in momentum.

3. What factors affect the momentum of a phonon?

The momentum of a phonon is affected by the mass and velocity of the atoms in the material, as well as the temperature and density of the material. Additionally, the presence of impurities or defects in the crystal lattice can also influence the momentum of phonons.

4. How does the momentum of a phonon impact heat and sound propagation?

The momentum of a phonon determines its ability to transfer energy and propagate heat and sound through a material. A higher momentum phonon will be able to travel further and transfer more energy before scattering, resulting in a more efficient energy transfer and faster heat and sound propagation.

5. Can the momentum of a phonon be controlled or manipulated?

Yes, the momentum of phonons can be controlled and manipulated through the use of materials with specific crystal structures and properties. This is an area of ongoing research in the field of phononics, with potential applications in thermal management and phononic devices.

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