What is Phonon: Definition and 106 Discussions

In physics, a phonon is a collective excitation in a periodic, elastic arrangement of atoms or molecules in condensed matter, specifically in solids and some liquids. Often referred to as a quasiparticle, it is an excited state in the quantum mechanical quantization of the modes of vibrations for elastic structures of interacting particles. Phonons can be thought of as quantized sound waves, similar to photons as quantized light waves.The study of phonons is an important part of condensed matter physics. They play a major role in many of the physical properties of condensed matter systems, such as thermal conductivity and electrical conductivity, as well as play a fundamental role in models of neutron scattering and related effects.
The concept of phonons was introduced in 1932 by Soviet physicist Igor Tamm. The name phonon comes from the Greek word φωνή (phonē), which translates to sound or voice, because long-wavelength phonons give rise to sound. The name is analogous to the word photon.

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  1. S

    I Phonon emission : Discrete event or a process with inner detail?

    If I understand correctly, when an electron drops to a lower energy state and emits a phoTon, this is a discrete or "atomic" event in the sense that it can't be meaningfully broken down in terms of more detailed sub-processes or interactions. Now in the case of phoNon emission, it is also...
  2. R

    Phonon Density of States (PDOS) at Gamma Point

    Hello everyone! I'm trying to replicate phonon density of states (PHDOS) diagrams for some solids using Quantum Espresso. The usual way I do it is the following one: scf calculation at minima (pw.x) Calculation of dynamical matrix in reciprocal space with nq=1 or 2 (ph.x) Calculation of...
  3. C

    I Wave in phonon as "forward and backward" movement vs temperature

    My first question here, so maybe not adequate or in the wrong topic, excuse me. I try to understand vibrating light harvesting antenna in biochemistry but it is a question of physics. We talk about a molecule with an emission spectra peak of about 650 nm. In classical physics electrostatic and...
  4. chikchok

    Phonon density of states and density of states of free electrons

    In the following pdf I tried to calculate the density of states of free electrons and phonons. First, I found the free electron DOS in 1D, it turns to be proportional to (energy)^(-1/2) and in 2D it is constant. However, I am not sure I found the DOS for phonons in the second part of the...
  5. dRic2

    I What Happens to Energy When Phonons are Damped?

    If you go beyond the harmonic approximation, phonons can not be thought as independent quasiparticles anymore and phonon-phonon interactions are taken into account. This eventually translates into the fact that phonons frequencies get renormalized ( ##\omega \rightarrow \omega^′ +i\nu ##)...
  6. matteo137

    Continuous-variable cat state - phonon number mean and variance

    I found the mean to be $$\langle n\rangle=\vert\alpha\vert^2 \tanh(\alpha^2)$ and $\langle n^2\rangle=\vert\alpha\vert^2 \left( \alpha^2\sech(\alpha^2)^2 + \tanh(\alpha^2) \right)$$. Do you know if there is any reference where I can check if this is correct?
  7. dRic2

    I Phonon Number Conservation in a Single Mode Oscillation Experiment

    Suppose I prepare an experiment where I excite a single mode of oscillation of the lattice, that is something like ##u(x, t) = Ae^{i(kx-\omega t)} ## (in the classical limit). The energy corresponding to that mode should be ##E = \frac 1 2 \rho L^3 A^2 \omega^2 ##. If I equate this equation to...
  8. C

    I Physical question about Phonons

    Hi, I have a question regarding Phonons and daily experience: Let's say I have a table and I hit it, does it mean Phonons were created where I've hit on the table? Meaning: By hitting the table, I'm giving energy to it, this energy goes to the motion of the table atoms, and this motion of the...
  9. S

    A Do acoustic phonons disappear in charge density wave states?

    In most standard exposition of (the mean-field theory of) charge density wave (CDW), phase and amplitude fluctuations are introduced as the collective excitations. Kohn anomaly in the acoustic phonon dispersion is also mentioned as temperature goes from the above till the CDW transition...
  10. phzrosmary

    A Raman spectroscopy and the phonon confined in the Brillouin zone

    Hello everyone, I need some confirmation on something: As far as I understood, the raman spectroscopy measures the inelastic scattering of a photon in a medium through the absorption or the emission of a phonon in the medium. The energy and the momentum is conserved...
  11. S

    I Phonon Mass: Understanding its Sign and Effects on Gravity

    What is the sign of phonon mass? A substance of uniform composition, in a field of gravity, has pressure increasing downwards. This causes the compressibility to decrease downwards - and speed of sound to increase downwards. In a gradient of downwards increasing velocity, a wave propagating...
  12. fluidistic

    I How come electrons and phonons lead to the heat equation?

    Phonons on their own lead to the common heat equation. One sees that for example in insulators or non doped semiconductors. However in metals (or conductors), the electrons are the ones that are mostly responsible for the heat transfer, which extremely surprisingly to me, is also of the form of...
  13. charlesmartin14

    A Nuclear - lattice coupling

    Mossbauer spectroscopy is an example of a nuclear (de)excitation coupling to a lattice phonons Are there any other examples of this phenomena ?
  14. S

    I Is there a frequency cutoff for Debye theory of capillary waves?

    I calculated the energy density of capillary waves with Debye method (pretty much Debye model in 2D), and I assumed there is a frequency cutoff for capillary waves as well. However, when I checked my work with solution I was quite surprised that the solution suggests there is no such a cuttoff...
  15. E

    A Change in phonon dispersion with pressure

    Hi, I'm looking into how phonon dispersion changes with pressure analytically and need to know how the atomic spacing in copper changes with pressure in order to model the crystal. I can't find any helpful papers online :( Any help would be appreciated thanks e
  16. H

    I Is this a Stirling number of the second kind?

    I saw this paper that talks about phonon sidebands, multiphonon relaxation, and phonon-assisted energy transfer. I was skimming through each of the equations, but I have problem understanding the formulation of some of them, for example Equation (3.17): g_{\pm }(t) = \int d\omega...
  17. H

    A Phonon-assisted energy transfer between lanthanides

    Dear all, I am not understanding well the "phonon-assisted" energy transfer between lanthanide ions and I need some clarifications. There is a theoretical work by Miyakawa and Dexter (doi:10.1143/JPSJ.32.1577) which explains how phonon plays a role in transferring energy from one (4f-state of)...
  18. S

    Why is Sn a better conductor than Pb?

    Homework Statement Hi guys, I'm currently writing an extended essay in Physics looking at the effect of percentage composition of Sn has on the electrical resistivity of SnPb Solder. I've noticed that Sn is listed as being a better conductor than Pb, despite trends of periodicity and have been...
  19. Demystifier

    A Detecting Single Phonons: Is It Possible?

    Is it possible to detect a single phonon? If yes, can it be detected at a well-defined position?
  20. M

    Solids with different sound velocity at diffrent tempratures

    i work on phononic crystals and i want to find solids with diffrent sound velocities and mass density in diffrent temprature i can just find BST but i need more matherials please help me my friends best regards
  21. M

    I 1D Phonon density of state derivation

    I'm having some trouble finding consistent results for the derivation of the 1D phonon density of state. I'm applying periodic boundary conditions to a 1D monatomic chain. I can work through and find that D(K)=L/(2π). This is the same result as given by Myers (1990, p. 127). Myers uses only...
  22. Auto-Didact

    A Decoherence-free phononic BEC quantum devices?

    Howl et al. 2016, Quantum Decoherence of Phonons in Bose-Einstein Condensates Anyone in the field of quantum information/quantum computation wish to comment on such an approach for building a quantum computer?
  23. C

    A Phonon energy and atomic vibration energy

    When we say that a phonon vibration mode has an average energy <E> are we saying that all atoms (or harmonic oscillators) in a piece of matter (eg. a nanoparticle) will also has that energy, or that the piece of matter as a whole will have that energy ? In the second case the amplitude of the...
  24. A

    I Phonon energy in absorption of indirect band gap

    Does phonon required a minimum energy in the absorption process of an indirect band gap, and why?
  25. A

    I Can the Planck equation be derived by considering phonons?

    As far as I understand, phonons are just thermal vibrations of atoms in a lattice and blackbody radiation is just the radiation emittied due to thermal oscillations accelerating the atoms back and forth. Is there any example of a derivation of the Planck equation from considering black body...
  26. otaKu

    Solid State A good book to learn about phonon dispersion relation

    So I see them in the books labelled as accoustic and optical phonons but I don't seem to find a comprehensive treatment of the matter for a beginner who doesn't know a thing about the dispersion curves. I'd prefer not to dwell too much into the mechanical treatment if possible since I just need...
  27. J

    I Mandel-Q Parameter and Phonon Statistics

    Hi, I'm struggling to understand how the Mandel-Q parameter (MQ) can be used to evaluate the quantum dynamics of a single trapped ion. A trapped ion has a quantised degree of motional freedom so can be discussed in terms of the phonon. Im studying the dynamics of a trapped ion which is subject...
  28. klotza

    The Interaction of Sound and Light - Comments

    klotza submitted a new PF Insights post The Interaction of Sound and Light Continue reading the Original PF Insights Post.
  29. L

    A Difference between an optical and an acoustic phonon

    Hello friends. My question consists two parts, 1-What is the difference between an optical and an acoustic phonon? 1-What are the conditions by which we can decide the type of phonon i.e optical or acoustic phonon ? Hope to get the reply soon.
  30. I

    How does doping affect the degeneracy of semiconductors?

    Hello, I am new to the forum, so I am directly stating my questions. 1)What determines the density of states of Phonons in a semiconductor? 2)Does degeneracy of semiconductors depend only on doping? Thanks
  31. philton

    Phonon Lorentz Invariance in Superfluids - Papers?

    It is said phonon(not photon) in superfluid experiments could also produce similar upper-limit speed effect which I'm not sure if that's also Lorentz invariant. Another problem is that I can't dig out those paper that demonstrates this kind of effect. Anyone ever seen any of this paper? Thanks..
  32. G

    Phonon neutron scattering

    Consider a monoatomic 1-D chain of atoms (only acoustic branch). What happens with the inference of the dispersion curve through neutron scattering? In one dimension, conservation of momentum dictates $$ k'=k+K_s $$, if k_s is the phonon momentum vector and we only consider processes where a...
  33. K

    Electron-Phonon interaction

    I am reading Frohlic's paper on electron-phonon interaction. Frohlic.http://rspa.royalsocietypublishing.org/content/royprsa/215/1122/291.full.pdf Here author has introduced the quantization for complex B field in this paper and claimed to have arrived at the diagonalized form of the...
  34. K

    What is an approximate amplitude of a phonon?

    I am aware that phonons are lattice vibrations - and that the amplitude of vibration would depend on the temperature. But say, at room temperature what would the order of magnitude of these lattice vibrations be ? In particular, in continuum limit these phonons can be treated as elastic...
  35. J

    Phonon dispersion Points/Modes question

    Hey all, I am trying to recreate the phonon dispersion plot of the paper below http://ocw.mit.edu/courses/electrical-engineering-and-computer-science/6-730-physics-for-solid-state-applications-spring-2003/projects/ProjP21.pdf The problem is I do not know what the Tau, L, and X on the x-axis...
  36. S

    Phonon frequency spectrum distribution

    hello every one , I want to know how we get phonon frequency spectrum theoretically by using three modes and dispersion relation, can anyone explain it. for example it is phonon energy correspond to density of state how it is obtain?
  37. Anand Wilson

    Can we break the hydrogen bonds in DNA with Phonon?

    Double stranded DNA are bind with hydrogen bonds in between the nitrogenous bases, Usually we use high temperature for denature,so can we break the hydrogen bonds with phonon because shorter wavelength give rise to heat, weather it is possible to denature the DNA?
  38. W

    Number of phonon modes possible

    Hi! How exactly is the relationship between number of atoms in the basis of a bravais lattice, and the number of possible phonon modes? So, for example, if you have 2 atoms in a basis you get 3 acoustical and 3 optical modes in 3 Dimensions. But why exactly is this? Do you need to set up the...
  39. J

    Optical phonons in fcc-lattice

    Aluminium has an fcc structure, which is a simple cubic lattice with four Al-atoms in the basis. On the other hand, diamond has a diamond structure, which is a simple cubic lattice with 8 atoms in basis. Now, diamond has optical modes in addition to acoustical, while Aluminium does not. What...
  40. L

    Acoustic phonon lifetime is larger than optical phonon?

    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!
  41. S

    YBCO Phonon Frequency: Hole Doping .2, 75-70°K @ 70°K

    I was hoping someone could tell me the phonon frequency of the electrons for YBCO with hole doping of about .2 and a critical temperature of around 75-70°K at about 70°K. An answer in Hz would be preferred, or failing that, in cm-1 with the wave speed. Also, might the Kohn anomaly influence the...
  42. U

    What does this length represent?

    I was doing some calculations earlier and tried the ratio between a metal's fermi temperature ##T_F## and debye temperature ##\theta_D##: \frac{T_F}{\theta_D} = (6 \pi^2)^{\frac{1}{3}} \left( \frac{\lambda}{a} \right) where ##\lambda = \frac{\hbar}{2 m_e c}## and lattice spacing is ##a##. I...
  43. R

    Electron - Phonon scattering, deriving the contribution to

    ... electron transport. 1. Homework Statement Electron - Phonon scattering, derive the contribution to electron transport. Homework Equations Trig. The Attempt at a Solution Am I being REALLY stupid here, I can't see how the equation matches the triangle. If you resolve KF' doesn't KF'...
  44. R

    Difference between phonon and electron excitation

    Homework Statement Homework Equations Debye approximation. The Attempt at a Solution For the first question (a) he has taken the lowest energy transition to be 0.2eV. (3eV-2.8eV with k=0) For the second question (b) he has taken the lowest energy transition to be at k=1. (it works out as...
  45. W

    How many acoustic and optical modes are there in a 3D crystal with p atoms?

    Homework Statement Homework EquationsThe Attempt at a Solution Since it's 3D, I assume there's at least 3 acoustic modes and 3 optical modes? After all, the soundwaves/phonons must be able to travel in all directions. Further on, I know both longitudinal and transverse modes are possible...
  46. K

    Phonon Energy and Density of States

    Hi all, In Charles Kittel (Introduction to Solid State Physics) He writes : U (Total Phonon Energy ) = Σk∑p((ħ*ωk,p)/((exp(ħ*ωk,p/τ))-1)) I understand this, but then he integrate over k and multiply by density of states : U (Total Phonon Energy ) = ∑p∫dω*Dp(ω)*((ħ*ωk,p)/((exp(ħ*ωk,p/τ))-1))...
  47. F

    What are the physical implications of phonon softening?

    I am interested in how phonon softening would lead to changes in a crystals elastic properties but I don't understand what actually is the consequence of this. What would be affected by a reduction in energy to phonons in a crystal? My best guess would be a reduction in energy to phonons causes...
  48. R

    How to simplyfy a square root term? Phonon dispersion relati

    I'm having trouble simplyfying this, I guess there's a trick but for the life of me can't remember what it is. Here is what I have so far: ##\omega ^{2} = f\left ( \frac{1}{m}+\frac{1}{M} \right )-f(( \frac{1}{m}+\frac{1}{M} \right ))^{2} - \frac{4q^{2} a^{2}}{mM})^{\frac{1}{2}}## so I divide...
  49. L

    How's diffraction pattern modied by phonon perturbation?

    Hi there, I have a problem on phonon perturbation's effect on diffraction pattern. Assume atomic planes parallel to (100) of bcc lattice is periodically perturbed by phonon. How will diffraction pattern be modified as a result of such perturbation? Will we see any diffraction peaks in addition...