# Tagged Questions

Collective excitations in periodic, elastic arrangements of atoms or molecules in condensed matter, like solids and some liquids. They are quasiparticle quantum modes of vibration of elastic structures of interacting particles.

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### Why are numbers not consistent? (Identifying phonon's frequency)

I am trying to connect several facts between each other to acquire a consistent picture. Fact 1. Monolayers of tungsten disulphide $WS_2$ have hexagonal crystal lattice, and the first Brillouin zone ...
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### Does a degassed magnet weigh less than one that is not?

I learned matter with an electric current weighs more than matter with no current. Does that apply to magnetic material in the same way but with it's magnetic fields instead of electric current? A ...
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### phonon dispersion with random masses

In order to see how phonons should be affected by disorder, I've been playing around with a model involving a 1D chain of masses linked by springs, where the spring strengths are all the same but the ...
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### How does phonon scattering change the distribution function?

For a one-dimensional structure, we know that the modified distribution function has the following energy dependency in equilibrium: Z(\varepsilon)\,f(\varepsilon) = \dfrac{N_\text{1D}...
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### When do optical phonon branches arise?

As far as I understand from what I'm studying, only when you have more than one kind of atom in the lattice structure, will the phonon have an optical branch, or else it should not have an optical ...
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### Quantization of energy of phonons

when taking into account of energy of photons, the relationship $E=nh\nu$ stands because it is said that the Energy is proportional to the frequency of the electromagnetic wave, however when the ...
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### Help with the analytical solution for the dispersion relation of an elastic wave with wave vector k

I was studying Phonons and Lattice vibrations and came across the equation. I want the mathematical solution for this. $$M\frac{d^2u_n}{dt^2}=C[u_{n+1}+u_{n-1}-2u_n]$$ from here it is argued that ...
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### Has a phonon, a formal quasi-particle, ever been observed as a point particle?

Phonons are a nice tool to simplify the quantum-mechanical description of lattice vibrations by identifying the ladder operator of normal modes as creation operators of a certain quasi-particle. In ...
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### Phonon modes in one-dimensional monoatomic chain

I am familirazing myself with the lattice dynamics reading Ashkroft-Mermin (p2 ch 22). My question is what it the mathematics behind the deriviation $U^{harm}=1/2 K \sum_{n} [u(na)-u([n+1]a)]^2$ (22....
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### Monte Carlo, Non-polar optical phonon scattering?

I have a question on electron and non-polar optical phonon scattering in GaAs. Is it allowed to consider intravalley electron non-polar optical phonon scattering in L-valley of GaAs? I found in the ...
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### Why the lifetime of acoustic phonons is larger than that of optical phonons?

for example, in GaAs, the LA phonon lifetime can be ~850 ns, while LO phonon lifetime is only about 5 ps. Why such huge difference occurs? Thanks!
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### Is it possible to efficiently extract phonons from a lattice?

The population inversion generated in lasers occurs in multi-level atomic systems. As an example, the Nd:YAG energy diagram is shown below. The pump pushes the Nd ions up to the upper levels, and ...
I had a question regarding phonon spectrum in condensed matter. Consider a cubic lattice with '$p$' atoms per primitive cell. Consider the lattice plane used for derivation of the phonon spectrum to ...