Talk:Phonon

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)

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)

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 231906 (2005) ) - shepplestone 4-6-06

Having researched and examined the topic further, I have deleted the above statement as it is incorrect. shepplestone 23-11-06.

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)

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

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)