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.

Filter by
Sorted by
Tagged with
1 vote
0 answers
28 views
+50

Ratio between Stokes and anti-Stokes scattering amplitudes in Raman scattering

I'm trying to understand the amplitudes and the ratio between those of Stokes and anti-Stokes scattering in Raman scattering. I understand that from a Boltzmann distribution point of view, the ratio ...
user avatar
1 vote
1 answer
29 views

Quantum effects on phonon transport?

Phonons are the quanta of vibrations in a crystal lattice. As the name suggest, phonons are already a quantum phenomena but when studying heat transfer the phonons are mostly very classical (wave ...
user avatar
  • 2,789
0 votes
0 answers
21 views

How to make sense of phonon dispersion curves and dynamic stability?

I've been working on this material that I've been doing DFT calculations on and I've managed to obtain the phonon dispersion curves for it. Calculation for it took quite a while, but here it is: Now ...
user avatar
1 vote
1 answer
57 views

How to understand crystal momentum, its relation to translational symmetry, Noether theorem, and to symmetry breaking/Landau-Ginzburg theory?

This question continues from my another question How to understand critical points of the Brillouin zone, (in)direct bands of transition-metal dichalcogenides?, and is related to Is crystal momentum ...
user avatar
0 votes
0 answers
16 views

How to calculate the mass for phonon vacuum fluctuations?

I am studying this paper, the precise content of which isn't relevant for the question. In there, the authors consider quantized bulk vibrations in a diamond. As usual when quantizing such systems, ...
user avatar
1 vote
0 answers
31 views

What is the reduced mass of a diamond unit cell?

I am reading this paper to study so-called collapse models. However, the paper isn't really relevant to understand the problem here. In the paper, the authors are considering a bulk vibration (optical ...
user avatar
0 votes
0 answers
29 views

Why there is maximum $n$ ($n_{Debye}$) for mode counting in phonon?

Hi! I'm curious about the description in my textbook of maximum $n \rm (n_{debye})$ in mode counting for phonon. I can realize the $n$ has maximum, because $\lambda_n(min) = 2a(\rm{lattice-constant})$....
user avatar
1 vote
2 answers
38 views

Phonon, photon have chemical potential equal to zero

Hi I know the chemical potential of the phonon and photon is equal to zero. And I know the reason is the number of these particle isn't conserved. But I don't know why the number of the phonon isn't ...
user avatar
2 votes
1 answer
68 views

What is the mass of collective oscillations?

When you step through the procedure of deriving a phonon dispersion relationship for a given crystal structure (i.e. small oscillations from equilibrium, harmonic approximation, collective coordinate ...
user avatar
1 vote
1 answer
38 views

What is the relation between phonon anharmonicity and thermal conductivity?

The textbook says that: if the vibration of the lattice were harmonic, then the states of phonons would be orthogonal to each other. As a result, there would be no interaction between phonons, hence ...
user avatar
0 votes
0 answers
25 views

Density states of phonons with different speed at different directions:

I was trying to get the density of states $g(v)$ for phonons which have $2$ polarizations transversally, and $1$ polarization longitudinally. My approach: $$dN = \frac{1}{8} 4 \pi n^2 dn, \lambda = c/...
user avatar
  • 451
2 votes
2 answers
46 views

What prevents a "beam combiner" from being able to cancel out energy?

I understand that normally when two waves combine destructively this happens only in certain places; the energy doesn't disappear but is redistributed to other places where the interference is ...
user avatar
  • 338
0 votes
1 answer
67 views

Polaron transformation in quantum optics

I'm trying to understand the so-called polaron transformation as frequently encountered in quantum optics. Take the following paper as example: "Quantum dot cavity-QED in the presence of strong ...
user avatar
0 votes
0 answers
16 views

Drawing reciprocal space phonon vectors

I'm a bit unsure about how the crystallographic directions work with phonon momentums and reciprocal space. If I have a phonon that's travelling in some direction $[abc]$ in a cubic structure, I ...
user avatar
  • 410
12 votes
2 answers
1k views

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 ...
user avatar
  • 123
1 vote
0 answers
17 views

How to derive specific heat of a crystalline material from phonon density of states?

I have done a simulation of a crystalline material using DFT and have extracted its normal modes and its phonon density of states. Does anyone have an algorithm/code or a detailed resource that can ...
user avatar
  • 111
2 votes
0 answers
73 views

Electron transport in fluids VS solids ("structure factor" VS "phonons")

Assume to have a neutral plasma consisting of some ions $X^+$ in a neutralizing gas of electrons $e^-$. Imagine that the $X^+$ can be in a gaseous (G), liquid (L) or solid (S) phase. We want to ...
user avatar
  • 2,895
6 votes
4 answers
542 views

Why are phonons bosons if they cannot occupy the same eigenstate?

I am reading the The Oxford Solid State Basics and on pages 82-83 it appears the following: If a classical harmonic system (i.e., any quadratic Hamiltonian) has a normal oscillation mode at frequency ...
user avatar
  • 71
0 votes
0 answers
47 views

What is physical meaning of terms like "Two-particle continuum" and "two-particle density of state"?

I am reading this article arXiv:2011.06543 about interacting magnons and they plot two-magnon density of states given by equation $$ D_k(\epsilon) \propto \sum_{\gamma,\gamma'}\sum_q \delta (\epsilon -...
user avatar
4 votes
2 answers
134 views

Does free phonon propagator always vanish at zero momentum?

When discussing electron-phonon interaction, the simplest leading electron self-energy usually has only the simplest phonon bubble diagram and excludes the 'tadpole' diagram below with a phonon ...
user avatar
  • 3,047
18 votes
3 answers
3k views

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 ...
user avatar
  • 11.4k
0 votes
1 answer
71 views

Phonon-electron interaction in superconductors

I'm trying to understand the phonon-electron interaction in superconductors. I'm a high school student doing a project on superconductors and I can't find understandable information about it. Almost ...
user avatar
0 votes
0 answers
29 views

How does the $T^3$ dependence for the thermal conductivity from phonons get derived (and linear $T$ for fermions)? Does anyone have resources?

I've been trying to find the derivation of the $T^3$ contribution for phonons and a linear $T$ dependence for fermions as I have seen it being mentioned multiple times in some publications. So far I'...
4 votes
0 answers
54 views

Current State of Research on high $T_c$ Superconductors

After looking at these two RevModPhys articles, I have found myself perplexed by the current state of high $T_c$ superconductivity research. Seeing as I cannot find any SE articles more recent than 5 ...
user avatar
1 vote
1 answer
80 views

What are phonons actually?

I was reading about heat conduction in solids wherein it was stated that in crystalline solids heat conduction takes place via lattice vibrations. In relation to this, the word phonon was used. In ...
user avatar
0 votes
0 answers
13 views

LO vs. TO phonons in a quasi-2D polar crystal at $Gamma$ point

In a polar quasi-2D crystal like hexagonal boron nitride, there seems to be a finite energy/frequency difference between the in-plane LO and TO phonon modes at the center of the Brillion zone (the $\...
user avatar
0 votes
0 answers
18 views

Can "bare" TO phonons in polar materials exist by themselves, or are they always phonon-polaritons?

We know that transverse optical (TO) phonons in polar crystals couple to light strongly and can form hybrid light-matter quasi-particles called phonon-polaritons (solid lines in the figure below). My ...
user avatar
1 vote
1 answer
39 views

Partition Function from Dispersion Relation in Molecular Dynamics

I’ve seen there are ways to compute the dispersion relation of a crystal from molecular dynamics. An example of how to do this is discussed in this question: Computing phonon dispersion from molecular ...
user avatar
  • 11
0 votes
1 answer
137 views

Phonons vs Normal mode

What is the difference between Phonons and Normal mode? My professor told me that they are the same and that one can get the other from some derivation (I'm a bit unsure if he really said the '...
user avatar
  • 788
2 votes
1 answer
103 views

Electron phonon coupling field integral

I am stuck on the problem "electron-phonon coupling" part a in Altland and Simons page 187. There is a related question on PSE, but that concerns part b. Borrowing from the notation in the ...
user avatar
0 votes
0 answers
21 views

Phonon modes and Raman scattering /IR absorption

Why are some phonon modes Raman-active and other are IR-active?
user avatar
  • 1
2 votes
1 answer
425 views

Why is it possible for us to "hear" acoustic phonons, but not optical phonons?

The name itself suggests that we can hear acoustic branch of phonon modes (and not the optical branch), but other than that I do not see any reason whatsoever why we are able to hear them. In order to ...
user avatar
  • 1,515
0 votes
0 answers
44 views

What is a phonon and electron line width in phonon-electron interaction?

In case of phonon-electron interaction, I came across a term called "phonon linewidth", and I do not understand from where does it arises and what significance does it have. and why is it ...
user avatar
0 votes
0 answers
29 views

Reference request: Derivation of the $T^5$ dependence of resistivity from electron-phonon scattering?

The scattering of conduction electrons with phonons gives rise to a resistivity that varies with the temperature as $T^5$. Is there a simple textbook derivation of this? Where can I find this?
1 vote
1 answer
65 views

What's the difference between inelastic X-rays scattering and Raman scattering?

In solids, inelastic scattering of X-rays can produce or absorb a phonon, which is equivalent to saying that solid ends up in excited vibrational level ( or if it was in a vibrational level to begin ...
user avatar
0 votes
0 answers
31 views

Can visible light be used for measuring phonon dispersion relation?

As phonon dispersion realtions can be studied using inelastic scattering of neutrons with phonons and X-ray. So, can visible light be used to do so?
user avatar
2 votes
1 answer
165 views

Why do optical phonons have such a high frequency at $k=0$?

Can you give me some intuitive explanation of this? How is there any frequency when wavelength becomes almost infinite?
user avatar
1 vote
0 answers
34 views

Heat Conduction in Deformed Solids

I am working on a model for isotropic elastic solids and have to make a decision about whether heat conduction should be isotropic in the reference or deformed configuration. I have spoken to two ...
user avatar
1 vote
1 answer
66 views

Shortest wavelength of sound wave in solids

In the book Thermal Physics by Schroeder, it is mentioned that "sound wave in solids cannot have wavelengths shorter than twice the atomic spacing". I am wondering if this is related to ...
user avatar
  • 630
2 votes
0 answers
20 views

Rotational invariance constraints on potential

I have a question about Nayak's lecture note , page 20, above equation (2.1) 'Rotational invariance implies that it can only be a function of the symmetric combination, $$u_{ij}=\frac{1}{2}(\...
user avatar
  • 1,703
0 votes
0 answers
20 views

Can phonons induce non-$s$-wave superconductivity?

In BCS theory the interaction is considered isotropic and the result is an $s$-wave superconductor. Is it possible anyway for unconventional superconductors to have SC driven by phonons (I intend this ...
user avatar
  • 148
1 vote
1 answer
67 views

Standing wave and optical mode in a crystal

I want to understand how when the wavelength $ \lambda$ is equal to 2a, with a being the lattice constant, two neighboring building particles of the crystal move in opposite direction. The general ...
user avatar
  • 934
0 votes
0 answers
23 views

Interaction of nonpolar optical phonons with light

How optical phonons in nonpolar insulators, such as diamond, interact with light and cause absorption lines in the infrared region? An example is the picture from this book chapter, where phonon ...
user avatar
0 votes
0 answers
22 views

Isothermal Gruneisen parameter for Germanium?

If phonon density of states peak shifts are purely quasiharmonic, we have $\omega$(V(T)). If phonon density of states peak shifts shifts are purely anharmonic, we have $\omega$(T). Does anyone know if ...
user avatar
  • 23
1 vote
0 answers
50 views

Reality of dynamical matrix without inversion

Assume throughout this question that we are working with non-relativistic phonons in the harmonic approximation. The Hamiltonian for phonons in the harmonic approximation is usually taken to be the ...
user avatar
  • 971
-3 votes
1 answer
140 views

Normalization of phonon density of states

Analogous to electronic structure calculations, we can solve for dispersion band structure of phonons for lattices using harmonic lattice approx. And we can find the so-called phonon density of states ...
user avatar
  • 105
1 vote
2 answers
67 views

Book recommendation: Does anybody know a book adopting a more intuitive approach to the topic of Crystal Vibrations (phonons) than the Book by Kittel?

I have tried Simon's 'Oxford Solid State basics' and Kittel 8th edition but I am not impressed by both (I mean the content covered through Chapters 4 and 5 in Kittel)
1 vote
1 answer
163 views

Why isn't the quantization of the phonon wave vector due to quantum mechanics?

My text book in solid state physics (Kittel) states that the quantization of the phonon wave vector arises due to boundary conditions (periodic or hard wall) for the modes of oscillation, and I can ...
user avatar
  • 151
2 votes
2 answers
90 views

Picturing Phonons

Consider vibrations of a One-dimensional monatomic chain of atoms. What I'm trying to do is to picture phonons? First where I am? So I have a one-dimensional monoatomic chain. With little calculation, ...
user avatar
0 votes
1 answer
44 views

Writing down a Hamiltonian that couples spin and phonons

I am studying spin dynamics and am trying to write down a Hamiltonian that couples the spins with the phonons. I have the following interacting spin Hamiltonian $$H_{s}=\sum h_{i}S_{i}+H_{\text{...
user avatar

1
2 3 4 5
7