Talk:Phonon

Colors of graphs
Some colors are not easy to distinguish (especially shades of red/green). Please use proper and clear contrast that avoids doubt over "pretty" or fashionable colors.

On 1D normal mode
I think the simulation on 1D phonon is very helpful for beginner to have a better understanding of lattice waves. It would be better if the author can clarify that the mode depicted is a longitudinal mode. Also, is the simulation depicting mono-atomic crystal or diatomic crystal? It seems that sometimes the "atoms" come too close to one another, which does not happen in real systems because of strong repulsion between atoms when they are less than one atomic diameter apart.WingkeeLEE 02:13, 22 June 2007 (UTC)

It is interesting to note that the most highly electrical conductive elements are those with an odd Z atomic number, which might imply the ability of interatomic agitation to aid in the electron transfer process. For example, it's easy to rub an electric charge off of sulfur, but the accumulated material is also a very good insulator.WFPM (talk) 17:18, 26 April 2010 (UTC)


 * Odd electrons per unit cell means half full bands in band theory, which tends to make better conductors. Full bands don't contribute to conduction. Almost full bands contribute holes, for a positive Hall coefficient. Gah4 (talk) 07:47, 13 July 2019 (UTC)

Oversized .GIF
Anyone else annoyed by the 6mb animated GIF? While it is effective at demonstrating a point, isn't there something that can be done about such a massive bandwidth hog? 60.224.44.222 08:08, 19 August 2006 (UTC) (can't be bothered signing in)


 * To Canberra-based user in Australia who "can't be bothered" to sign in: (a not-too-effective way to get people interested in queueing up behind you on an issue). Anyway, no kidding on the 6 MB file size! I didn't want to visit this article or even link to it because it was so damn slow. Now fixed.  I used two applications on a Mac to convert the file into a version that is 4.7% the size of the original, is indistinguishable from the original in visual appearance, and which loads much faster. This version also has an interframe delay of 40 ms (v.s. the original’s 100 ms).  Including processing time for each frame, this new version advances from frame to frame in 45–50 ms (a frame rate of about 20–22.5 Hz on a typical computer), which yields a more fluid motion.   Greg L 14:28, 4 October 2006 (UTC)


 * I have only a general familiarity with solid state physics, but I think that the diagram could be clarified by identifying the variables omega, lambda, and a. I see down in the article that a refers to lattice spacing, and I assume omega has something to do with frequency, but because these variables are only 'semi-standard' within physics, I'd like whoever posted the gif to either explain what the variables are within the caption, or, tell me so I can add a couple of sentences identifying the variables. I think that's just good diagramming-etiquette.
 * Trumpetmeister 14:57, 29 March 2008 (UTC)

Is this an error?
"There is no energy gap for phonons" (under Dispersion Relation) - but then what about Phononic Crystals which do have energy gaps? - h2g2bob 11/11/05


 * I suspect you'll find they're photonic crystals... -- CYD


 * There are both, though phononic and photonic crystals are very similar (phononic crystals have gaps in the acoustic (long wavelength) dispersion curve I believe) - h2g2bob 12/11/05

You should also note that several devices have gaps within there phonon spectrums such as silicon nanowires and nanodots (See Applied Physics Letters, Volume 87, Article) ) - shepplestone 4-6-06

Having researched and examined the topic further, I have deleted the above statement as it is incorrect. shepplestone.

Please elaborate
I have read this article a few times and still only have a vague concept of phonons. Can we get some more detail (and layman's explanations) on these sections:

"According to a well-known result in classical mechanics, any vibration of a lattice can be decomposed into a superposition of normal modes of vibration."

Can we link to an article about this rule, or give a short explanation if none exist?

"Secondly, we treat the potentials V as harmonic potentials, which is permissible as long as the atoms remain close to their equilibrium positions. (Formally, this is done by Taylor expanding V about its equilibrium value.)"

The link to screened in the sentence above this one helps explain it, but the link to harmonic oscillator doesn't really explain to me what a "harmonic potential" is.

"As we shall see in the following sections, any wavelength shorter than this can be mapped onto a wavelength longer than a."

This seems similar to aliasing in discrete-time sampled signal processing. If the analogy is close enough, should it be mentioned? Also, analogies to vibrations in strings would help me in particular, but I don't know how close these analogies are, and if they would give the wrong idea.

I guess the rest I don't understand simply because I don't know quantum mechanics... - Omegatron 14:26, Jul 21, 2004 (UTC)


 * I think some of these have been addressed, but the entry definitly still needs some work (I'll see what I can do ;-). I like the aliasing analogy, it's exactly right (the points where the atoms are placed act like the points (in time) where the analogue wave is detected in digital streams.) --H2g2bob 02:10, 16 December 2005 (UTC)

--- Would it be possible to add some stuff about non-equilibrium processes, like thermal conductivity??

Thermal conductivity has a seperate page within wiki

correcting small erro
Shouldn't "k" be "k_sub_n" in the exponents of the two Fourier relations immediately following the "One-Dimensional Phonons" subheading? Marcusl 15:58, 15 February 2006 (UTC)

Phonons & sound
In my opinion the reference to the name of Phonons is wrong: Phonons do not give rise to sound in crystals, there is merely a resemblace in the process. Sound would assume frequencies at least remotely near the audable range, which is not the case with phonons (>8 orders of magnitude difference).
 * Phonons do indeed give rise to sound in crystals. Although the order of magnitude of the frequency for phonons is typically given in the terahertz, this is for shorter wavelengths near the Brillouin zone edge.  In the long wavelength limit, the dispersion relation for the acoustic phonon branch becomes linear.  The slope of the dispersion relation in the long wavelength limit is the speed of sound in the crystal.UrbanaAchiever 01:48, 5 June 2007 (UTC)
 * Well, first, we most often think of sound propagating in gases, but it also goes through liquids and solids. And once you have the physics of it propagating through solids, it is the same physics at low and high frequency. The velocity is much higher in solids, so you would need a really big crystal to get down to audible frequencies. The physics would be the same, though. Phonon is mostly used when quantum effects are important, which is low temperatures (when the more random effects die down). Gah4 (talk) 14:46, 21 June 2021 (UTC)
 * Well, first, we most often think of sound propagating in gases, but it also goes through liquids and solids. And once you have the physics of it propagating through solids, it is the same physics at low and high frequency. The velocity is much higher in solids, so you would need a really big crystal to get down to audible frequencies. The physics would be the same, though. Phonon is mostly used when quantum effects are important, which is low temperatures (when the more random effects die down). Gah4 (talk) 14:46, 21 June 2021 (UTC)
 * Well, first, we most often think of sound propagating in gases, but it also goes through liquids and solids. And once you have the physics of it propagating through solids, it is the same physics at low and high frequency. The velocity is much higher in solids, so you would need a really big crystal to get down to audible frequencies. The physics would be the same, though. Phonon is mostly used when quantum effects are important, which is low temperatures (when the more random effects die down). Gah4 (talk) 14:46, 21 June 2021 (UTC)

Billiard ball model of the atmosphere
If one models air and air molecules as a lot of billiard balls in constant chaotic motion, then how does sound propagate through air? Are phonons associated with nitrogen and oxygen molecules, as they are with metal molecules? It seems it would be sort of Rube Goldbergian (like the board game Mousetrap) for sound to be carried and transferred between so many billiard balls in constant chaotic motion, when one is speaking to someone across the room.

I have read that air molecules at room temperature move about as fast as a jetliner; and that the average path lenght of an air molecule at room temperature is less than a meter. User: McTrixie --71.124.219.87 17:20, 27 August 2006 (UTC)

Some of them do move as fast as a jetliner, but some do not. They are distributed on a well known function called the "Maxwell–Boltzmann distribution". Sound is a statistical phenominon, because of the great many molecules involved, and hence behaves very well, even though each individual molecule seems to be very incapable of transmiting sound. On the whole, the millions and billions of molecules manage it collectivly.

Why?
It's easy to think of waves in a lattice, but I still don't see why they would qualify as a (quasi)particle. Presumably physicists invented/discovered phonons because they are a useful description of the world, but when do they behave like particles? —Ben FrantzDale 06:05, 19 January 2007 (UTC)


 * For instance in inelastic scattering experiments (Brilloiun scattering, Raman scattering, neutron scattering etc.) they behve like particles. User:Matthias_Buchmeier


 * This is similar to the question of describing light as an electromagnetic wave or as a stream of photons. At lower frequencies, the wave description works best, at higher frequencies particles. Gah4 (talk) 07:54, 13 July 2019 (UTC)

Phonons = bosons?
Hello,

This article seemingly contradicts boson by stating that phonons are bosons with integer spin, whilst the boson article states that bosons are particles with integer spin. This would make phonons=bosons, where my understanding of phonons is that they are purely propagation modes, where bosons are actual particles (where the word particle makes sense in quanta.

My understanding is insuffificent to declare this as correct, but does anyone have a definitive answer? User A1 14:08, 29 January 2007 (UTC)


 * anything with integer spin is in a group called the boson's, anything with half integer spin is in a group called hadron's, hence everything is either a boson or a hadron, in quantum mechanics ANYTHING with energy is a wave and so has a frequency and everything with frequency is a particle. so people are hadronic particles! the simplest observable indication of which of these groups something is in comes from the fact that hadrons can't pass through each other, when bosons can, since classical waves, like vibration, can, they are always bosons.

Asplace 11:19, 2 February 2007 (UTC)


 * So would I be correct in saying that the integer spin comment in phonon is superfluous? User A1 14:07, 2 February 2007 (UTC)


 * well you could actually read that last sentence in the header as, phonons are bosons BECAUSE they have integer spin. which is the definition of a boson, but seems to me ok if you assume the reader needs to be told that.
 * However i'm not sure the whole of the second paragraph isn't redundant, its trying to explain some general principles of QM, not really specific to phonons, a reader might be better of clicking the link to quanta at the top and reading about QM/superposition etc. there. this description is not the clearest i've come across. For example "they acquire certain particle-like properties when the lattice is analysed using quantum mechanics" how can an analysis cause properties? QM came about because people were already seeing particular properties in waves and needed to explain them, put simply, QM invents the concept of a wave/particle and says every wave and every particle is one of these, and it was a mistake to ever of thought they weren't. of course the maths used before QM doesn't suddenly stop working, but has clearer applicability restrictions.
 * Asplace 17:12, 2 February 2007 (UTC)

Re: Asplace who says anything with half-integer spin is a hadron. THIS IS INCORRECT. A hadron is a particle that can interact via the Strong interaction. You can have hadronic bosons (mesons). A FERMION is a particle with half-integer spin. Hadronic fermions are called baryons. Therefore all particles are either bosons or fermions, and may or may not also be a hadron. An example of a half-integer spin particle that is not a hadron is the electron. Such non-hadronic fermions are called leptons.86.133.152.185 13:33, 24 May 2007 (UTC)

Phasons?
I hoped to find here something about phasons which apparently are a special case of phonons existing in more complicated (e.g. incommensurate) structures. At a recent discussion on quasicrystals they were descibed as a misunderstanding, with the suggestion that 'phason' is in fact an adjective (and thus 'phasonic' is a pleonasm). Perhaps phasons should be mentioned briefly here and linked to separate article that somebody will write.195.96.229.83 10:12, 23 February 2007 (UTC)

Different masses?
¿why always the masses are the same in the solution of phonons? In many systems, the masses are not ordered neither the same.

The mass used is that of the crystalline unit cell which will always be the same. If the masses are not ordered you do not technically have a phonon since the whole concept is dependent on the existence of a perfectly ordered unit cell periodic in all directions. —Preceding unsigned comment added by 24.30.105.9 (talk) 07:45, 15 November 2007 (UTC)

Hermitian
Would standing waves be Hermitian ? Is this article supposed to be in sync with the French one? Arnero 05:55, 1 September 2007 (UTC)

Diagram in dispersion relation
In the dispersion relation section there is talk of a diagram, however I don't find it depicted in the article. I think including it would be very helpful in better understanding the section. —Preceding unsigned comment added by 86.198.1.156 (talk) 07:53, 30 October 2007 (UTC)

Still not fixed. "The blue, violet, and brown curves are those [...]" If nobody rectifies this in the next few days, I'll go ahead and remove the diagram references myself. 86.143.122.161 (talk) 12:37, 30 December 2007 (UTC)

The references are still there. In my opinion, one should not simply remove them. Instead, the missing diagram should be added or, to avoid clutter, an article that has a similar diagram must be linked here. So far, I have not been able to find such article. I think I could draw the diagram myself, but I am not familiar enough with the subject to explain it as clearly as this article needs. 82.147.167.179 (talk) 13:24, 13 January 2009 (UTC)

Can somebody fix some curves please? 87.64.35.12 (talk) 08:34, 25 May 2010 (UTC)

It would be nice if someone made said diagram. The issue was addressed as early as 2007, so may I ask why no-one has fixed it since? --Korot (talk) 20:03, 5 February 2011 (UTC)

Total Rewrite ?
My understanding is that an Wikipedia article ought to be readable by the average person, say, a high school student. I am a scientist and at 10 am, with no coffee in me, I can't read this article.Cyclopiano (talk) 18:19, 29 January 2008 (UTC)


 * I agree - the article needs to be made more accessible, at least to someone familiar with similar theory of light. HiraV (talk) 15:02, 16 November 2009 (UTC)


 * I agree too... the content of this article seems to me the material for a manual (wikibooks?) rather than an encyclopaedia (p.s. the lack of caffeine in a physicists blood stream at 10am does not support the validity of your comment though :)) Profeta (talk) 17:09, 20 April 2010 (UTC)


 * If people do a rewrite, I sure hope this article (or something quite like it) remains conveniently available. I also suggest that it remain editable like a Wikipedia article.  Phonons just aren't simple.  The article does give me a rough intuitive sense of what phonons are, which is an achievement.  But I don't claim to understand very much of the article, and my background isn't typical for Wikipedians.  Several decades ago, I passed a course in mineralogy (for geologists) and a 1-quarter introduction to quantum mechanics.  So, long ago, I heard about Hamiltonians, even though I've never done anything with them since then.  I got to the article from the article on cristobalite, about which I learned a little bit, decades ago.  Oaklandguy (talk) 22:58, 1 February 2014 (UTC)
 * I'm a scientifically literate lay person, and I find the article incomprehensible. The theory and detail in the article is useful for those that can make sense of it, but it needs an expanded lead and an overview section that explains the concept without jargon or mathematics. WP is an encyclopedia, not a textbook. --Ef80 (talk) 20:28, 2 July 2016 (UTC)
 * I suppose so, but it is mostly quantum mechanics. According to Feynman (who got a Nobel prize doing it), "Nobody understands quantum mechanics", so I am not sure we can expect high school students to understand it. High school students are expected to believe in, and sort-of understand, photons. That light is made up of particles that travel though vacuum or many materials, even without really understanding electromagnetism or Maxwell's equations. But vibrations are something we think we understand, and especially their non-quantum properties. Photons tell us that there is a smallest amount of light that we can have, at a give frequency. Phonons tell us that there is a smallest amount of vibration we can have, at a give frequency. Somehow, though, since we find vibration more understandable, quantization of it is less understandable. Gah4 (talk) 14:57, 21 June 2021 (UTC)
 * I suppose so, but it is mostly quantum mechanics. According to Feynman (who got a Nobel prize doing it), "Nobody understands quantum mechanics", so I am not sure we can expect high school students to understand it. High school students are expected to believe in, and sort-of understand, photons. That light is made up of particles that travel though vacuum or many materials, even without really understanding electromagnetism or Maxwell's equations. But vibrations are something we think we understand, and especially their non-quantum properties. Photons tell us that there is a smallest amount of light that we can have, at a give frequency. Phonons tell us that there is a smallest amount of vibration we can have, at a give frequency. Somehow, though, since we find vibration more understandable, quantization of it is less understandable. Gah4 (talk) 14:57, 21 June 2021 (UTC)
 * I suppose so, but it is mostly quantum mechanics. According to Feynman (who got a Nobel prize doing it), "Nobody understands quantum mechanics", so I am not sure we can expect high school students to understand it. High school students are expected to believe in, and sort-of understand, photons. That light is made up of particles that travel though vacuum or many materials, even without really understanding electromagnetism or Maxwell's equations. But vibrations are something we think we understand, and especially their non-quantum properties. Photons tell us that there is a smallest amount of light that we can have, at a give frequency. Phonons tell us that there is a smallest amount of vibration we can have, at a give frequency. Somehow, though, since we find vibration more understandable, quantization of it is less understandable. Gah4 (talk) 14:57, 21 June 2021 (UTC)

link to insulating solids
Should the link "insulating solids" in the first paragraph be to electrical insulation rather than thermal insulation? Igwood (talk) 04:26, 23 November 2008 (UTC)
 * Seems to have been changed to link to both. Do note, though, that heat travels through electrical conductors (metals) better than non-metals, and for good reasons. In any case, both are important, and especially when considering phonons. Gah4 (talk) 15:01, 21 June 2021 (UTC)
 * Seems to have been changed to link to both. Do note, though, that heat travels through electrical conductors (metals) better than non-metals, and for good reasons. In any case, both are important, and especially when considering phonons. Gah4 (talk) 15:01, 21 June 2021 (UTC)

Relation to photons?
Is not heat electromagnetic energy? Then, wouldn't that mean that all phonons are photons? I mean if we are talking about heat, and phonons are the particles of heat, then wherever there are photons there are phonons. Tcaudilllg (talk) 08:11, 9 February 2009 (UTC)
 * In short: no - heat is not electromagnetic energy. Read the Heat article for details, but in summary: heat may describe the energy transferred between objects at different temperatures (by any mechanism, of which electromagnetic radiation is but one), or, less formally, the energy "in" an object contributing to its temperature (e.g. the kinetic energy of its component particles). Phonons are (modes of) physical vibration in a regular lattice of particles (i.e. they are MECHANICAL vibrations, not electromagnetic vibrations). Phonons, being mechanical vibrations, carry energy, and so can transport energy; in this context they might be described as "particles of heat", but in that case there are several quite different kinds of "particles of heat" (e.g. photons; individual atoms / ions; individual sub-atomic particles; gravitons ...).FredV (talk) 14:15, 27 July 2009 (UTC)
 * It is more complicated than that, but the answer is still no. Photons are the carrier of the electromagnetic force, and so are responsible for holding molecules and crystals together. However, radiant heat, mostly far-IR, is photons. Convection is motion of different molecules in a gas or liquid. Conduction of heat is mostly phonons. Energy can exchange between the different types, and usually does. Consider a nitrogen molecule in the air, spinning around with thermal energy. We tend to think that things can spin at any rate we want them to, but no. Molecular rotation is quantized, such that they can only spin at certain speeds. At low temperature, there is a slowest speed that they can spin. However, polarized molecules will couple to the electromagnetic field, and so photons. You can't get away from either of them.Gah4 (talk) 15:14, 21 June 2021 (UTC)
 * It is more complicated than that, but the answer is still no. Photons are the carrier of the electromagnetic force, and so are responsible for holding molecules and crystals together. However, radiant heat, mostly far-IR, is photons. Convection is motion of different molecules in a gas or liquid. Conduction of heat is mostly phonons. Energy can exchange between the different types, and usually does. Consider a nitrogen molecule in the air, spinning around with thermal energy. We tend to think that things can spin at any rate we want them to, but no. Molecular rotation is quantized, such that they can only spin at certain speeds. At low temperature, there is a slowest speed that they can spin. However, polarized molecules will couple to the electromagnetic field, and so photons. You can't get away from either of them.Gah4 (talk) 15:14, 21 June 2021 (UTC)
 * It is more complicated than that, but the answer is still no. Photons are the carrier of the electromagnetic force, and so are responsible for holding molecules and crystals together. However, radiant heat, mostly far-IR, is photons. Convection is motion of different molecules in a gas or liquid. Conduction of heat is mostly phonons. Energy can exchange between the different types, and usually does. Consider a nitrogen molecule in the air, spinning around with thermal energy. We tend to think that things can spin at any rate we want them to, but no. Molecular rotation is quantized, such that they can only spin at certain speeds. At low temperature, there is a slowest speed that they can spin. However, polarized molecules will couple to the electromagnetic field, and so photons. You can't get away from either of them.Gah4 (talk) 15:14, 21 June 2021 (UTC)

Vandalism
Someone did a search-and-replace and replaced all instances of 'phonon' with 'photon', both in the article and the discussion page. I have fixed this. Nightrose (talk) 23:47, 10 June 2009 (UTC)

Quantisation
The explanation of quantisation of wavelength for phonons arising because of the lattice spacing seems simple enough, but I can't understand why this necessarily leads to quantisation of phonon energy. Why can a phonon of a given wavelength not take on a range of amplitudes (and hence a range of energies)? Andipi (talk) 11:50, 16 August 2009 (UTC)


 * E=hf and so E=hc/lambda as c=f*lambda, hence the energy is constant for each given wavelength. HiraV (talk) 15:02, 16 November 2009 (UTC)


 * I had exactly the same question and after reading (what I could of) the article was starting to think energy wasn't quantised at all for phonons, which seemed pointless. Not until I got here did it make any sense. I agree with your comment below - the opening leads the reader down the wrong path and I think it needs to be improved (I would say "fixed" but the whole crystal lattice and diagram thing made sense to me).--Adx (talk) 09:38, 1 June 2010 (UTC)


 * Increased amplitude mean more phonons in the same quantum state. (Remember, they are bosons.) As usual for QM descriptions, macroscopic sized objects have very large N (number of atoms, and so possible modes), and at normal temperatures, the modes are well populated. The quantum steps are small enough to look continuous. At low temperatures, quantum effects are more visible. Gah4 (talk) 08:05, 13 July 2019 (UTC)

Definition
I think the page should be started differently; phonons are defined not as the modes of vibration but the quanta of energy that these modes carry - this may lead to confusion. Phonons are to lattice vibration as photons are to electromagnetic radiation - individual fundamental quanta of energy. Should I change the opening of the page? HiraV (talk) 15:02, 16 November 2009 (UTC)

No Merger from Light scattering
I do not support the suggestion that the discussion of lattice vibrations and light scattering should be transferred to this general page on the description and mathematics of phonons. The brief description of thermal motion in elastic solids is essential there in order to develop a complete understanding of the mechanisms of Brillouin scattering (& sound absorption) by density fluctuations and microstructural defects in condensed matter. As pointed out there, light scattering has made possible the study of molecular processes from time intervals as short as 10−11 sec. This is one particular application amongst a number of subjects related to phonon transport.

Thus, there is no reason to support this merger. Rather, the main page on phonons should be clearly referenced there. logger9 (talk) 04:20, 25 June 2010 (UTC)

An error: the momentum is not k=πnj/Na but k=2πnj/Na
An error: the momentum is not k=πnj/Na but k=2πnj/Na

Read any book of quantum chain please. — Preceding unsigned comment added by 82.139.116.215 (talk) 00:55, 20 October 2011 (UTC)
 * To explain more explicitly, the periodic boundary condition requires x_N+1 = x+1. Allowing k to be odd multiples of πnj/Na violates this condition.  Physically, the longest possible wavelength is the length of the chain, Na.  It looks like the previous treatment was done with non-periodic boundary conditions, despite the text's claim to the contrary.  Correcting k=πnj/Na to k=2πnj/Na left some inconsistencies in the limits on both the sums in x_j / p_j and the allowed values for n, which I have corrected.  I admit that summing from -N/2 to +N/2 makes for an ugly formula (which is why I removed the \matrix formatting, it was getting very crowded).  Going from 0 to N would be equivalent, but I think using the symmetric interval is a more intuitive representation of left- and right-traveling waves.  — Preceding unsigned comment added by 128.205.65.123 (talk) 00:51, 26 October 2011 (UTC)
 * This is reminding me of the difference between the Fourier (exponential) transform and the Fourier cosine transform. More specifically (in the case of crystals) DFT vs. DCT. The boundary conditions are different, and in the case of DCT, the lowest wavelength is twice as long. Periodic boundary conditions are nice, as you don't have to worry about surface effects. Gah4 (talk) 15:22, 21 June 2021 (UTC)
 * This is reminding me of the difference between the Fourier (exponential) transform and the Fourier cosine transform. More specifically (in the case of crystals) DFT vs. DCT. The boundary conditions are different, and in the case of DCT, the lowest wavelength is twice as long. Periodic boundary conditions are nice, as you don't have to worry about surface effects. Gah4 (talk) 15:22, 21 June 2021 (UTC)
 * This is reminding me of the difference between the Fourier (exponential) transform and the Fourier cosine transform. More specifically (in the case of crystals) DFT vs. DCT. The boundary conditions are different, and in the case of DCT, the lowest wavelength is twice as long. Periodic boundary conditions are nice, as you don't have to worry about surface effects. Gah4 (talk) 15:22, 21 June 2021 (UTC)

Interpretation of phonons using second quantization techniques
An edit on September 22 by user Cesaranieto (see copied details below) seem to have made a large difference to this section of the article. For example, the user added new/extra notation including $$l_k = \sqrt{\hbar/m\omega_k}$$, that is not at all necessary and changed the operators from a's to b's for no obvious reason. The most troubling change though is the definition of the ladder operators. I have worked out the commutation relation for the operators as defined and it does not give the correct value. With the old definition of the a's, the commutation does work out correctly such that $$[a_k, a_k^{\dagger}] = 1$$. Of course, it is possible that I made a mistake, and I have been unable to find a suitable primary source containing the answer. Nonetheless, unless someone can explain why the change was made, I will revert to the original version tomorrow.

The offending change (if I judge correctly, my mediawiki-fu is not too strong) 22:58, 22 September 2012‎ Cesaranieto (talk | contribs)‎. . (34,165 bytes) (+173)‎

Micah Stoutimore (talk) 01:01, 16 October 2012 (UTC)

phonons and vibrations, quanta and waves
A lot of the results on this page (animations, dispersion relations) seem to have to do with lattice vibrations in general. I think it might be nice to have a separate article that discusses lattice vibrations in general (acoustic vs optical vibrations, Brilloin zones, dispersion etc.), so that the phonon article can deal with issues that specifically involve the quantization of lattice vibrations. This would be analogous to how there are separate pages for electromagnetic radiation and photon. Nanite (talk) 13:36, 29 January 2014 (UTC)
 * I agree, it will be great for the readability of both articles and make it easier to structure all the information. JanJaeken (talk) 10:11, 30 January 2014 (UTC)

LO vs TO vs LA vs TA
It would be nice if this article could have more information explaining how to distinguish these types of modes when looking at a phonon dispersion spetra. For instance I've been told that acoustic modes always start at zero frequency at k=0 due to Bose symetry. Also there is typically LO-TO splitting so the TO mode is at lower frequency (in salts, one can prove the LST relation). I've been told LO modes typically have a larger slope than TO modes. It's hard to find reference that prove these points hold in general, though. I've heard a good reference is "electrons and phonons" by Ziman, but I don't have access to it at the moment. Danski14(talk) 22:10, 23 February 2015 (UTC)

Not quasiparticles?
I don't understand what this means: Even though phonons are often used as a quasiparticle, some popular research has shown that phonons and rotons may indeed have some kind of mass and be affected by gravity 1. What does "often used as" mean? Are they quasiparticles or not? As I understand the rest of the article, a phonon is a quasiparticle by definition, and nobody has suggested they are physical particles. 2. The sentence seems to imply that quasiparticles having mass is a contradiction. But the second sentence of the quasiparticle article mentions the example of an electron in a semiconductor that acts like a quasi-electron with different mass. So evidently the notion that quasiparticles cannot exhibit mass is erroneous. It wouldn't make sense to speak of quasiparticles if they didn't exhibit measurable physical properties such as mass.--85.247.151.151 (talk) 12:08, 12 March 2019 (UTC)
 * I agree with you and will remove the offending statement. The cited reference makes no attempt to say it is not a quasi-particle, it does not even mention quasiparticles in any context. Additionally, as you point out, that is misusing the term quasiparticle. A quasiparticle is any particle that does not share all characteristics shared by the underlying particle. An electron with a slightly different mass or charge would be a quasiparticle, an electron with no mass is also a quasiparticle, which does make sense and is useful at times in HEP. Footlessmouse (talk) 23:45, 14 August 2020 (UTC)
 * I suppose, but if you try too hard, I suspect everything in quantum mechanics is a quasiparticle, so they might as well just all be particles. That is, in wave-particle duality, we don't say wave-quasiparticle duality. Are photons quasiparticles? Otherwise, it is a reminder not to look too closely. Since phonons have enegy, and energy is equivalent to mass, I suspect that means that they have gravitational mass, not that you could measure it. Gah4 (talk) 14:12, 1 May 2022 (UTC)
 * I suppose, but if you try too hard, I suspect everything in quantum mechanics is a quasiparticle, so they might as well just all be particles. That is, in wave-particle duality, we don't say wave-quasiparticle duality. Are photons quasiparticles? Otherwise, it is a reminder not to look too closely. Since phonons have enegy, and energy is equivalent to mass, I suspect that means that they have gravitational mass, not that you could measure it. Gah4 (talk) 14:12, 1 May 2022 (UTC)
 * I suppose, but if you try too hard, I suspect everything in quantum mechanics is a quasiparticle, so they might as well just all be particles. That is, in wave-particle duality, we don't say wave-quasiparticle duality. Are photons quasiparticles? Otherwise, it is a reminder not to look too closely. Since phonons have enegy, and energy is equivalent to mass, I suspect that means that they have gravitational mass, not that you could measure it. Gah4 (talk) 14:12, 1 May 2022 (UTC)

second quantization
There are many in the second quantization section, pretty much on each equation. As well as I know, it is described in most upper level undergraduate, and many graduate level QM books. I suppose we could specify one, but if most have it, it shouldn't be needed. Gah4 (talk) 08:10, 13 July 2019 (UTC)

I will write out proofs for these equations and remove the citation needed templates. If any other editors disapprove of this, I can just add an arbitrary reference to Griffiths or something (I will double check to make sure it has the info, of course, but Gah4 is correct, this is basic content found in most undergrad textbooks on the topic). Let me know what you think. Footlessmouse (talk) 00:04, 15 August 2020 (UTC)

The use of the term ladder operators in this section differs in terminology from creation and annihilation operators used elsewhere. I have rewritten a chunk of this section already, but left this quirk, should we make it consistent, or point out they are the same thing? Footlessmouse (talk) 07:41, 15 August 2020 (UTC)
 * As well as I know it, ladder operators is the collective term for both, as they walk up or down the ladder of states. Shorter than saying creation and annihilation operators every time. Gah4 (talk) 14:06, 1 May 2022 (UTC)
 * As well as I know it, ladder operators is the collective term for both, as they walk up or down the ladder of states. Shorter than saying creation and annihilation operators every time. Gah4 (talk) 14:06, 1 May 2022 (UTC)

Reference to first mention considered
A recent article mentions “First proposed by Albert Einstein in 1907, phonons are packets of vibrational energy emitted by jittery atoms.” which seems to contradict or at least require an additional citation on the origin of phonons.

Article on recent advancements using phonons as a microphone which includes the mention of Einstein: https://m.phys.org/news/2019-07-physicists-particles-quantum-microphone.html

I have not researched this claim but opening up discussion on future changes to this page. Listre (talk) 21:16, 29 July 2019 (UTC)

typo?
I cannot understand this sentence: "It is customary to deal with waves in Fourier space which uses normal modes of the wavevector as variables instead coordinates of particles."

Should be 'instead of coordinates'? — Preceding unsigned comment added by 76.169.229.184 (talk) 16:21, 20 June 2021 (UTC)
 * It still sounds a little strange. Fourier space means frequency space. (Or spatial frequency, as the case may be.) But yes, they should be considered as ω and k (wave vector or wave number), and not as position and velocity (or time). Gah4 (talk) 15:30, 21 June 2021 (UTC)
 * It still sounds a little strange. Fourier space means frequency space. (Or spatial frequency, as the case may be.) But yes, they should be considered as ω and k (wave vector or wave number), and not as position and velocity (or time). Gah4 (talk) 15:30, 21 June 2021 (UTC)

atoms or molecules uniformly oscillates at a single frequency
The article says: atoms or molecules uniformly oscillates at a single frequency. It seems to me that the usual uncertainty principle should apply, and like photons, be a wave packet with a width (in frequency) and length (in time). If the width is narrow compared to other scales in the problem, I suppose single frequency is a good approximation. But that mostly only works when there are a large number in a mode. That is, when the phonon (particle like) explanation isn't needed. Gah4 (talk) 10:35, 29 December 2021 (UTC)
 * Regarding a recent edit, I was going to say this, but it seems I said it last year. Gah4 (talk) 14:03, 1 May 2022 (UTC)
 * Regarding a recent edit, I was going to say this, but it seems I said it last year. Gah4 (talk) 14:03, 1 May 2022 (UTC)

"Phononic Computing" listed at Redirects for discussion
An editor has identified a potential problem with the redirect Phononic Computing and has thus listed it for discussion. This discussion will occur at Redirects for discussion/Log/2022 May 12 until a consensus is reached, and readers of this page are welcome to contribute to the discussion. 1234qwer1234qwer4 19:59, 12 May 2022 (UTC)


 * The field is just taking off. Why was it deleted from this article? https://phys.org/news/2019-05-phonon-mediated-quantum-state-remote-qubit.html Hcobb (talk) 20:33, 12 May 2022 (UTC)

single phonon detection
A recent edit indicates that single phonons are not detectable, but a web search finds many papers on them. It is convenient that many photons have energies that we can detect, especially in the visible optical range. Partly that is because a single molecule in our eye needs to detect one. But low energy photons are not individually detectable, such as those at radio frequencies. And for phonons, higher frequencies are individually detectable, and low frequency ones not detectable. Gah4 (talk) 05:36, 10 June 2023 (UTC)

Origin of the name
The introduction tells us, without citation, that the concept of phonons was introduced in 1932 by Soviet physicist Igor Tamm. Does anyone know which publication this refers to?

On the other hand, the book Twentieth century physics, Vol. I (p.1302) tells us that the name phonon was introduced by Frenkel in his 1932 book Wave mechanics: Elementary theory to ridicule the notion of a photon. If someone has access to that book, it would be interesting to know exactly what Frenkel writes on the subject. Jähmefyysikko (talk) 06:14, 10 June 2023 (UTC)

superconductivity
This article says

Phonons have also been predicted to play a key role in superconductivity in materials and the prediction of superconductive compounds

whereas Britannica says

''phonons are essential in the phenomenon of superconductivity... In superconducting metals at sufficiently low temperatures, however, electrons—which ordinarily repel each other—slightly attract each other through the intermediate effect of phonons. The result is that the electrons move through the material as a coherent group and no longer lose energy through individual collisions. Once this superconducting state has been achieved, any initial flow of electrical current will persist indefinitely.'' Espoo (talk) 06:09, 19 August 2023 (UTC)
 * BCS theory uses phonons in its explanation. Among others, the transition temperature, Tc, is dependent on the isotope mass, which couples to phonons. Gah4 (talk) 09:18, 28 February 2024 (UTC)
 * BCS theory uses phonons in its explanation. Among others, the transition temperature, Tc, is dependent on the isotope mass, which couples to phonons. Gah4 (talk) 09:18, 28 February 2024 (UTC)

Individual detection
I removed: However, photons are fundamental particles that can be individually detected, whereas phonons, being quasiparticles, are an emergent phenomenon. For those interested, the removed reference is here. Gah4 (talk) 09:05, 28 February 2024 (UTC)