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Questions tagged [phonons]

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.

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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What is a phonon?

I am trying to understand intuitively what a phonon is, but for the moment I find it quite difficult (having a limited background in quantum mechanics, an undergraduate course in non-relativistic QM). In fact, I find it hard to formulate good…
doetoe
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Do gases have phonons?

A phonon is a quantized unit of sound; they are encountered when quantizing lattice vibrations in solids. Now, even an ideal gas supports sound waves, but in this case, interactions between atoms are weak. That makes it hard to imagine what a…
knzhou
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Is crystal momentum really momentum?

Almost every solid state physics textbook says crystal momentum is not really physical momentum. For example, phonons always carry crystal momentum but they do not cause a translation of the sample at all. However, I learned that in…
skywaddler
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How to get an imaginary self energy?

The Lehman representation of the frequency-dependent single particle Green's function is $$G(k,\omega) = \sum_n \frac{|c_k|^2}{\omega - E_n + i\eta}$$ where $n$ enumerates all the eigenstates of the system, $c_k$ is the overlap between…
Lagerbaer
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Phonon carries zero spin. Why?

photons and phonons both have polarization, we attribute spin 1 for photons but spin 0 for phonons. Why?
richard
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How similar are phonons and photons?

If you go through the definitions for "phonon" (or for an explanation of phonon), most of the text or articles make the analogy to photons: A photon is a discrete quantum of light. A phonon is a discrete quantum of vibration. Further, in this…
Himanshu
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Why are phonons quantized?

I'm a third year physics major taking an introductory subject on condensed matter physics. I'm trying to understand the concept of phonons in a 1D lattice. I understand the classical treatment of (1D) lattice vibrations (wikipedia has a derivation…
LittleJollyBoat
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Is sound a classical mechanic phenomenon or is it a quantum effect?

I am just curious because sound is longitudinal waves, meaning the energy is passed from one particle to another nearby particle and produces a wave that continues on until it reaches our ear as a sound wave or hits our skin as a pressure wave, so…
user6760
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Rest mass of phonon: is this concept definable?

Phonons are obtaied by non-relativistic quantization of the lattice vibration. The dispersion relation is given by $\omega=c_s k$ where $c_s$ is the velocity of sound. What can we say about the mass of the phonon? I think it is not possible to…
SRS
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Why is crystalline graphite black yet shiny?

I am unable to find images of pure crystalline graphite with high confidence, but based on various sources I believe that it should actually be both black and shiny, in the sense that it reflects much less visible light than a white piece of paper,…
user21820
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Why do we not use the Schrödinger equation/standard QM to describe phonons (or other quasi particles)?

We were just taught about phonons in solid state physics class. Last year we did QM and now we are starting QFT as well. Phonons are excitations of a condensed matter field. I thought that we would be using the Schrödinger equation (SE), but no. It…
gemmima
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The difference between optical phonons and acoustic phonons in terms of energy absorption

Why can the energy of a photon be directly absorbed by an optical phonon but not by an acoustic phonon？
G2AQUESTIONBOY
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Why zero chemical potential does not allow the Bose-Einstein Condensation of Phonons?

Here I report the reasoning from which my question comes. According to: O.V. Misochko, Muneaki Hase, K. Ishioka, and M. Kitajima. Transient bose–einstein condensation of phonons. Physics Letters A, 321(5–6):381 – 387, 2004. one cannot have the…
Chaos
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Why don't low frequency phonons scatter electrons in a superconductor?

A crystal at any finite temperature has phonons, as longer wavelength phonons require less energy to be excited. It seems that the electron (or cooper pair composite particle) wave would be scattered by phonon-induced inhomogeneities in the…
Kevin Kostlan
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Could gravitons be quasiparticles like phonons?

The Einstein field equation $$ G_{\mu \nu} + \Lambda g_{\mu \nu} = {8 \pi G \over c^4} T_{\mu \nu} $$ basically says: $$ \text{curvature of spacetime} \sim \text{stress-energy tensor} $$ The stress-energy tensor is most often written in the…
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