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.
359
questions
1
vote
1
answer
21
views
Phonon Distribution Factor in Phonon Emission Rate
The rate at which a phonon with wavevector $\vec{q}$ is absorbed is given by
$$\frac{1}\tau \propto n(\hbar \omega(\vec{q}))$$
This is pretty obvious to me. The more phonons there are the more often ...
- 53
0
votes
0
answers
21
views
How do peaks arise in phonon detection from IR spectroscopy reflectivity measurements?
I want to clarify my understanding of the shape of phonon signatures in IR spectroscopy reflectivity measurements. Intuitively, at resonant frequencies, the photons hitting the sample should be ...
- 1
1
vote
2
answers
79
views
Optical and Acoustic Phonons: Choice of Unit Cell
According to my book, phonon dispersion relation for three dimensions, the number of acoustic phonons is 3 per unit cell while the number of optical phonons is 3(M-1) where M is the number of atoms in ...
- 73
0
votes
0
answers
28
views
Sign of Wave Number and Angular Frequency
In chapter 9, page 78, of The Oxford Solid State Physics Basics by Steven Simon, the author claims an ansatz given by $$e^{iwt-ikna}$$ as a solution of 1D monatomic chain of atoms connected by ...
- 73
2
votes
0
answers
67
views
How can two phonons be entangled when the atoms in the crystal are not?
It is my understanding that you can use phonons to make a gaussian packet, which would behave like a quantum particle. I also believe that you can make two such packets and entangle them, that is ...
2
votes
2
answers
39
views
Exciton-phonon coupling Hamiltonian
I'm reading this article about coherent exciton transport in photosynthetic light harvesting and the role of quantized vibrations. Along the way, I came across a section where the article claimed the ...
- 616
1
vote
1
answer
67
views
How are topological materials considered "protected by the gap" if the electrons couple to gapless phonons?
My understanding is that Hamiltonians are usually classified topologically by whether they can be continuously transformed into each other without closing the band gap.
I then usually hear claims ...
1
vote
1
answer
39
views
Momentum conservation in phonon-photon scattering event
I am following a discussion from Kittel´s Introduction to Solid State Physics in the subchapter ‚phonon momentum‘:
We have two different conservation laws of momentum in a crystal:
Total momentum is ...
- 399
6
votes
1
answer
218
views
Wave equation for phonons
Question: What is the relativistic (quantum) wave equation that governs that motion of phonons?
My Attempt(s): The phonon Hamiltonian is given by, $$\mathscr{H} = \dfrac{1}{2}\sum_n \left(p_n^2 + \...
- 658
1
vote
0
answers
27
views
What is the physical explanation behind the softening of the Kohn anomaly mode associated with charge density waves?
From the literature I've read, Fermi-nesting is a mechanism that can lead to charge density wave (CDW) formation in which a gap is created in the Fermi surface (which correspons with a nesting ...
- 21
1
vote
0
answers
30
views
Can phonons experience a photoelectric-like effect? [closed]
In a crystal lattice, could phonons experience some form of the photoelectric effect?
0
votes
1
answer
41
views
What happens to the optical branch solution in the limit of same masses in a diatomic chain?
For a monoatomic chain, we get the following dispersion relation:
$\omega(k) = \sqrt{\frac{4 \kappa}{m}\sin^2{\left(\frac{ka}{2}\right)}}$,
where $m$ is the atom mass, $\kappa$ is the spring constant, ...
- 7
0
votes
1
answer
32
views
One-dimensional diatomic chain phases
In my solid state book, when deriving the dispersion relation of a diatomic one-dimensional chain, the author makes the following Ansatz for the oscillation of the first (x) and seond (y) atom in the ...
- 7
2
votes
1
answer
58
views
Is the formation of crystal due to internal symmetry or spacetime symmetry?
In the contexts of field theory, we have internal symmetries and spacetime symmetries. Referring to crystal, people would say it is due to space translation symmetry. However, I don't think the ...
- 31
0
votes
0
answers
31
views
Potential energy of phonons as harmonic oscillators
I'm trying to derive the phonon hamiltonian which is anologous to a collection
of independent harmonic oscillators. I've already have kinetic energy but I'm kinda stuck on the potential energy. The ...
- 289
0
votes
0
answers
10
views
Is the temperature dependence for electron phonon scattering the same between plasma oscillations and DC transport?
I am examining the temperature dependence of electron phonon scattering in the case of a metal responding to an AC field (forming a plasma oscillation). I have found that for DC transport, the ...
- 123
16
votes
6
answers
5k
views
Why are phonons quantized?
I'm a third year physics major taking an introductory subject on condensed matter physics. I'm trying to understand the concept of phonons in a 1D lattice.
I understand the classical treatment of (1D) ...
- 230
0
votes
0
answers
97
views
The importance of the Debye frequency for superconductivity and the relation of it to critical temperature and the superconducting gap
I am preparing for an exam in superconductivity at the moment and one of the questions to prepare for is the one mentioned in the title. My preliminary answer would be that the Debye frequency $\...
0
votes
0
answers
22
views
Relation between low-energy modes of phonon and infinite oscillator limit
The Klein-Gordan equation is often described as coupled oscillators, taking the limit $l\rightarrow \infty $ to reduce to wave equation with linear dispersion relation. I'm considering here the ...
- 11.3k
2
votes
1
answer
32
views
Laser on metal surface: What happens in terms of photons, plasmons, phonons and their interactions?
I'm trying to better understand what exactly happens when a laser beam hits a surface (apart from reflection). Say I have a thick gold surface (could be coated with gold nanoparticles if that helps) ...
- 255
0
votes
0
answers
17
views
Is it possible that a phonon having the same momentum $q$ after an scattering event?
We went through different phonon scattering events in my lecture. We looked at: Surface, surface roughness, impurity and "Umklappen" scattering. All those events changed the wavevector q of ...
- 31
1
vote
0
answers
33
views
Phonon modes and atom vibrations vs temperature
My understanding is that number of phonon modes depends on the number of atoms in a system and will be gradually populated with increasing temperature until Debye temperature. At the same time, atoms ...
- 11
0
votes
1
answer
20
views
Can Kohn anomaly be driven by parameters other than temperature?
The Kohn anomaly is the singular behavior of phonon softening in materials, for which a mean-field theory is the BCS type and is usually described to be driven by lowering the temperature till some ...
- 3,352
0
votes
0
answers
53
views
Frequency dependent Purcell effect for a broadband emitter
How do I model the following system?
I have an NV-center in diamond with a broad fluorescence spectrum, centered at roughly 700 nm with a FWHM of 100 nm. (The NV-center is a defect in diamond, it can ...
- 33
0
votes
0
answers
31
views
How do you Determine the Fastest Vibrational Mode of a Crystal?
I understand that a crystal's vibrational modes are Phonons and have a minimum wavelength that is limited by twice the equilibrium separation between neighbouring atoms. But I don't understand how you ...
- 343
0
votes
1
answer
30
views
Why holes are better in storing both valley and pseudospin information?
Recently I attended a class about transition-metal dichalcogenides (TMDC) and, during the lecture, the professor said that holes are better than electrons in storing both pseudospin and valley ...
0
votes
2
answers
74
views
How do phonons and electron-electron interactions break phase coherence of electrons? Also, do they break time reversal symmetry?
When considering electron scattering, I appreciate that phonons and electron-electron interactions need to be considered in a different light to scattering from a static, disordered potential.
With a ...
- 141
5
votes
0
answers
138
views
Free acoustic phonon propagator
For fun I am trying to find the propagator of a free acoustic longitudinal phonon, using the vectorial displacement field.
The Hamiltonian for our system is
$$ H_0 = \sum_{\vec{q}} \omega_{\vec{q}} ( ...
- 103
0
votes
2
answers
67
views
Can phonon follow similar curve as photons follow in blackbody radiation? [closed]
I recently came to know about phonons, and how similar they are to photons, like both are bosons and mu = 0 in both cases, only difference between them as far as I know is there spin states (phonons ...
- 11
0
votes
0
answers
35
views
Effective mass of a quasi-particle
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 ...
- 79
0
votes
1
answer
92
views
Reading a graph for dispersion relation of normal modes in 3D lattice
I'm trying to interpret graphs of this type. In this example, dispersion relation $\omega = \omega(k)$ for some waves corresponding to lattice vibrations in GaAs are shown.
What is uncomprehensible to ...
- 495
1
vote
1
answer
49
views
Maximum of oscillator displacement due to one phonon
let's say I have a mechanical mode with frequency $\omega$ and effective mass $m$. I put one phonon in that mode and want to get an estimate (or ideally) calculate the maximum displacement of my mode (...
- 79
3
votes
1
answer
141
views
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 ...
1
vote
1
answer
60
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 ...
- 3,967
0
votes
0
answers
149
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 ...
- 51
1
vote
1
answer
187
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 ...
- 207
0
votes
0
answers
35
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, ...
- 79
1
vote
0
answers
47
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 ...
- 79
0
votes
0
answers
53
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 $\lambda_n(min) = 2a(\rm{lattice-constant})$....
- 21
1
vote
2
answers
85
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 ...
- 21
2
votes
1
answer
97
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 ...
1
vote
1
answer
62
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 ...
- 11
0
votes
0
answers
28
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/...
- 588
3
votes
2
answers
112
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 ...
- 370
1
vote
1
answer
443
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 ...
- 51
13
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 ...
- 133
1
vote
0
answers
25
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 ...
- 111
2
votes
0
answers
109
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 ...
- 3,765
6
votes
4
answers
663
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 ...
- 71
5
votes
2
answers
224
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 ...
- 3,352