Timeline for Do gases have phonons?
Current License: CC BY-SA 4.0
35 events
| when toggle format | what | by | license | comment | |
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| Nov 14, 2023 at 21:19 | answer | added | Toby C | timeline score: 2 | |
| Jun 28, 2019 at 18:57 | history | edited | knzhou | CC BY-SA 4.0 |
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| Feb 14, 2017 at 6:41 | vote | accept | knzhou | ||
| S May 15, 2016 at 23:58 | history | bounty ended | CommunityBot | ||
| S May 15, 2016 at 23:58 | history | notice removed | CommunityBot | ||
| May 10, 2016 at 2:19 | answer | added | Xcheckr | timeline score: 5 | |
| May 10, 2016 at 1:16 | comment | added | Rococo | @MaximUmansky this is an interesting point. The experiment you mention sounds just like a liquid analog of acousto-optic modulation, which is indeed usually discussed in terms of phonon-photon interactions. I think maybe this is a case of the common situation in which once you quantize one thing (photons, in this case), it is often helpful (although rarely strictly necessary) to treat everything it interacts with as being quantized too. | |
| May 9, 2016 at 23:23 | answer | added | Maxim Umansky | timeline score: 1 | |
| May 9, 2016 at 16:56 | comment | added | Maxim Umansky | I remember my undergraduate physics lab class when we excited a standing wave in a volume filled with water, and then shined a laser beam on this periodic structure. The laser beam interacted with it as with a diffraction grating; and scattering of photons could be described in terms of photon-phonon interaction, i.e., writing energy and momentum conservation for a two-particle collision gives the right answer for the laser beam scattering angle. Doesn't this say that the phonon paradigm is appropriate here? | |
| May 9, 2016 at 7:04 | answer | added | valerio | timeline score: 12 | |
| May 9, 2016 at 5:40 | answer | added | R. Rankin | timeline score: 2 | |
| May 8, 2016 at 13:02 | comment | added | Ian | Momentum eigenstates of the system. By momentum eigenstates of the nuclei do you mean to separate the nuclei from the electrons, or are you just referring to momentum of a single atom vs total momentum? | |
| May 8, 2016 at 12:59 | comment | added | lnmaurer | @Ian Are they "momentum eigenstates of the system", "momentum eigenstates of the nuclei", or are the two the same? It makes sense that they are "momentum eigenstates of the system", but I don't see how "momentum eigenstates of the nuclei" follows from that unless there's a crystal lattice. | |
| May 8, 2016 at 3:47 | comment | added | Ian | @lnmaurer The phonons in liquid helium ARE the momentum eigenstates of the system. In fact if you look at Feynman's phonon-roton ansatz for the low energy collective excitations in liquid helium, you can see that these are momentum eigenstates, and that they form a variational guess for the true phonon momentum eigenstates at small wavevectors. | |
| May 8, 2016 at 3:40 | comment | added | Ian | I don't think a truly ideal gas supports sound waves. You need interactions between particles to support sound waves in a gas. In a quantum ideal gas I don't think it makes sense to talk about phonons either since the collective excitations are simply products of single particle excitations. I guess if you look in the literature you should be able to learn about phonons in imperfect gases. | |
| May 8, 2016 at 3:30 | comment | added | lnmaurer | @IlyaLapan Yes, by definition the minimum phonon wavelength has to be bigger than the distance between atoms, but that's only because the minimum wavelength is twice the distance between the atoms; the phonon wavelength can be comparable to the atomic spacing, right? | |
| May 8, 2016 at 2:05 | answer | added | Rococo | timeline score: 17 | |
| May 7, 2016 at 22:38 | comment | added | Ilya Lapan | I think the big thing about phonon approximation is that the typical wavelength of vibration has to be bigger than the distance between atoms. | |
| S May 7, 2016 at 22:35 | history | bounty started | knzhou | ||
| S May 7, 2016 at 22:35 | history | notice added | knzhou | Draw attention | |
| May 7, 2016 at 17:04 | comment | added | Mikael Kuisma | @lnmaurer Ok, with phonons in my statement above, I meant only a system with lattice translation symmetry from which a phonon band structure emerges (with energy and momentum axes). And certainly one can have vibrational quasiparticles with finite lifetime in liquids too. And of course the phonons in solids have finite lifetime and are quasiparticles too. | |
| May 7, 2016 at 3:58 | history | tweeted | twitter.com/StackPhysics/status/728796015357218816 | ||
| May 6, 2016 at 15:30 | comment | added | lnmaurer | @Mikael Kuisma I'd say that phonons are a more general concept than "momentum eigenstates of the nuclei". After all, there are phonons in liquids (most famously in liquid helium), and I doubt that they can be described as "momentum eigenstates of the nuclei". | |
| May 6, 2016 at 15:24 | answer | added | lnmaurer | timeline score: 0 | |
| May 5, 2016 at 23:30 | comment | added | Mikael Kuisma | About phonons being 'quantized unit of sound'... Well, that is sort of not entirely wrong, but some care is required. Phonons are based on energy and momentum eigenstates of the nuclei. They go up to terahertz regime, and that is not normally considered sound. There are longitudinal and transverse phonons, sound is usually considered only longitudinal. Sound is a transport phenomenom where as phonons are stationary eigenstates. Hence, sound is a superposition of phonons with varying linear combination coefficients. Usually the group velocity at q=0 is enough to characterize speed of sound. | |
| May 5, 2016 at 19:10 | comment | added | CuriousOne | @AnubhavGoel: My answer would be negative, but I am not competent enough in theory to give a conclusive answer. My gut tells me that with thermodynamic forces at play the coherence time is too small to get useful quantum results. | |
| May 5, 2016 at 14:05 | comment | added | Anubhav Goel | @CuriousOne So , should that question their be edited or an answer be added there. Although its not been answered there, Otherwise it would be duplicate. I see it isn't answered here even. | |
| May 5, 2016 at 11:18 | comment | added | CuriousOne | @AnubhavGoel: And the linked post doesn't answer that question. A gas is not a disordered solid and that's all they are talking about in the answers, unless I missed something. | |
| May 5, 2016 at 11:11 | comment | added | Anubhav Goel | @CuriousOne The first statement in question there " >Do sound waves in a gas consist of phonons?" is just what OP asks in question. | |
| May 5, 2016 at 9:48 | comment | added | CuriousOne | @AnubhavGoel: That's the same post and it's about disordered solids, not gases... the difference is that in gases the restoring forces are thermodynamic, in solids they are potentials. | |
| May 5, 2016 at 9:27 | comment | added | Anubhav Goel | Related: physics.stackexchange.com/q/7129 | |
| May 5, 2016 at 9:22 | comment | added | Anubhav Goel | Ah! On googling I found highlights that someone picked this topic. But, unfortunately I did not see Keenan Pepper in his answer said he cannot answer that part. :p. | |
| May 5, 2016 at 9:18 | comment | added | CuriousOne | I have not seen a quantum mechanical treatment of acoustic waves in thermodynamic gases, but that's probably not the end of the story. Did you look into excitations of Bose Einstein condensates? | |
| May 5, 2016 at 9:08 | comment | added | CuriousOne | @AnubhavGoel: Disordered solids are not the same as gases or liquids and the answers don't apply. | |
| May 5, 2016 at 8:06 | history | asked | knzhou | CC BY-SA 3.0 |