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
0 votes
0 answers
17 views

Can we use Density Functional Theory (DFT) to calculate the second and third-order force constants of a slab?

If we aim to compute the surface phonon lifetime of a Cu(111) surface, the second and third-order force constants are essential (to put in Boltzmann transport equation). However, to my knowledge, it ...
James's user avatar
  • 1
1 vote
0 answers
22 views

Phonon and the coupling to electrons

I am new to looking at phonons, especially in relation to their use in coupling to electrons. Phonons can be defined as the treatment of vibrations in a crystal lattice. There can be different types/...
Lb762's user avatar
  • 31
1 vote
0 answers
26 views

Why don't we see the transverse waves with a phonon lattice dynamic while we see them with linear elasticity theory?

Let's say that we have a lattice with particles sitting on the nodes. Each particle $n$ has neighbors $\bar n$: $$\dfrac{d^2\boldsymbol u_n}{dt^2}=-K\sum_{\bar n}\boldsymbol u_{\bar n}\tag{1}$$ The ...
Syrocco's user avatar
  • 973
0 votes
0 answers
12 views

Exploring Phonon Dispersion in Two-Dimensional Materials: Analytical Techniques and Mode Identification

How can one analyze the phonon dispersion of 2D materials like graphene to discern specific curves corresponding to particular phonon modes, such as acoustic or optical, as well as longitudinal and ...
Farah Shehzadi's user avatar
0 votes
0 answers
26 views

Evaluate convergence of force constants in crystal with increasing cutoff

I have a crystal with 2 atomic species, A and B. I'm interested in the interatomic force constants (IFCs) and I have a program that computes them for a given supercell. Basically, I have to provide ...
chewingram's user avatar
1 vote
1 answer
52 views

What is the relation between linear elastic theory and phonon transport?

I am reading about Boltzmann equation and I am having a hard time making a link between elastodynamics and phonon equations. Clearly there should be a limit where both are one and the same, isn't it? ...
Mauricio's user avatar
  • 5,346
1 vote
0 answers
29 views

Can one experimentally confirm whether the effective attractive interaction is retarded and its relation with superconductivity?

It's widely believed that in convential BCS superconductors, only after taking the retardation effect into consideration the weak attractive interaction mediated by phonons can overwhelm the strong ...
Black Monolith's user avatar
1 vote
1 answer
67 views

Why acoustic phonon dispersion cross $\omega=0$ at $k=0$?

When I am learning about phonons, it is taught that acoustic phonons necessarily have $\omega=0$ at $k=0$. while optical phonons have a finite $\omega$ at $k=0$. But I am confused about two things: ...
physstudent11's user avatar
1 vote
0 answers
25 views

Born Oppenheimer approximation and screening

In the Born-Oppenheimer approximation we take the full Hamiltonian of a solid, given by $$H = T_e + T_{ion} + V_{ee} + V_{e-ion} + V_{ion-ion}$$ where the T are the kinetic energy of electrons and ...
F.Burton's user avatar
  • 153
1 vote
0 answers
42 views

Phonons from Born-Oppenheimer approximation vs plasma oscillations

I'm trying to connect to different pictures used when talking about phonon dispersion relations in metals. Both can be found in standard textbooks, for example Ashcroft & Mermin. In the first, one ...
F.Burton's user avatar
  • 153
1 vote
0 answers
45 views

Why does the phonon displacement have an overall factor of $i$?

I'm going through Mahan's book on Many Body Physics, and I'm a bit confused about one of his claims. First he expresses the position of an atom as $$\textbf{R}=\textbf{R}_{i}^{(0)}+\textbf{Q}_i$$ ...
Redcrazyguy's user avatar
1 vote
2 answers
72 views

Sound as an energy source [closed]

A sound wave is a massless packet of energy much like a photon. Would it be feasible to use these energy packets to generate electricity in the same way as solar panels. I am thinking of panels about ...
Michael Mcgarry's user avatar
1 vote
2 answers
107 views

Do certain quasi-particles really have negative mass?

Do phonons for example really have negative mass or does it just seem like they have negative mass? Could one use the negative mass of certain quasi particles to meet the negative energy requirements ...
Peter's user avatar
  • 133
0 votes
1 answer
81 views

Why each normal mode is treated as a harmonic oscillator in Debye's calculation of specific heat?

So in Einstein's calculation of specific heat each oscillator is assumed to be vibrating with same frequency and its average energy is given by hv(n+1/2) where n is bose factor. Debye said that ...
Mr. Wayne's user avatar
  • 343
0 votes
1 answer
139 views

How is the energy of phonon modes $\left(n+\frac{1}{2}\right)\hbar \omega_k$ when each atom in the mode has $\left(p+\frac{1}{2}\right)\hbar \omega$?

I'm having trouble understanding the quantisation of energy in normal modes of lattice vibrations. Stating Kittel : The energy of a lattice vibration is quantized. The quantum of energy is called a ...
Rishab Navaneet's user avatar
0 votes
0 answers
46 views

Can continuous translation of Wigner crystal be described by charge neutral density excitations?

In a two-dimensional electron gas (2DEG), under conditions where electron-electron interactions predominate over kinetic energy contributions, the ground state is a Wigner crystal. This crystalline ...
aj_01100110's user avatar
0 votes
0 answers
38 views

Picturing a normal mode of vibration of the monoatomic lattice in 1D that is either in-phase nor completely out-of-phase

For a monoatomic lattice of $N$ atoms in one-dimension, the ratio of the displacements of two consecutive atoms at the $(n+1)$th and the $n$th site is given by $$\frac{u_{n+1}}{u_n}=e^{ika}$$ where ...
Solidification's user avatar
0 votes
1 answer
288 views

What are soft phonon modes?

In chapter 4 of Charles Kittel's Introduction to Solid State Physics, a problem titled "soft phonon modes" asks us to derive the dispersion relation for the following setup: a 1d crystal ...
Jono94's user avatar
  • 596
0 votes
0 answers
18 views

Soliton in non-degenerate polymer

I just started reading about the conduction mechanism in polymer. From what i read, polarons are used as method of charge transportation in non-degenerate polymer. While for degenerate polymer, both ...
taqiuddin yusri's user avatar
5 votes
1 answer
256 views

Mermin-Wagner theorem and SSB in 2D: is there sound in low dimensional solids

The Mermin-Wagner theorem states that there cannot be any spontaneous symmetry breaking happening in systems with short range interactions below dimension 3. Moreover, we know that Goldstone boson, ...
Syrocco's user avatar
  • 973
1 vote
0 answers
48 views

Lennard-Jones potential can be valid at 0.2 Angstrom Distance between two particles?

I have modeled a graphene-vacuum-graphene system. Here two graphene sheets connected by L-J potential through vacuum gap (Phonon transfer through vacuum). I have simulated it considering 0.2 to 10 ...
Md. Jahid Hasan Sagor's user avatar
0 votes
0 answers
29 views

Debye-Waller Factor in the case of isotropic fluctuations

I am reading through Girvin & Yang Ch. 6 (pg. 91), they mention that the Debye-Waller factor $$-2\Gamma(\vec{q})=-\langle\langle(\vec{q}\cdot\vec{u}_j)^2\rangle\rangle$$ (where the positions of ...
umklapp's user avatar
0 votes
1 answer
57 views

Possibility of calculating phonon dispersion from crystal structure

Is it in principle possible to calculate the dispersion relation of phonons in a crystal from the crystal structure?
I'm Batman's user avatar
0 votes
0 answers
12 views

How to induce the Phonon Effective mode mass?

i don't know the phonon effective mode formula. Who knows why effective mode mass formula have the following form? https://doi.org/10.1103/PhysRevB.104.L060103 PDF
Y. S. Lym's user avatar
1 vote
0 answers
40 views

The definitions of coherent phonons and acoustic phonons

I found that the definition of coherent phonon: A femtosecond laser pulse can initiate collective, in-phase atomic motions in solids called coherent phonons. My question is: what is the difference ...
MathJacky's user avatar
1 vote
0 answers
50 views

At temperature $T>0K$, are all normal vibrational modes present simultaneously in a one-dimensional solid?

I am studying Debye theory of Specific heat. hyperphysics has this picture and there it says "Considering a solid to be a periodic array of mass points, there are constraints on both the minimum ...
Dinesh Katoch's user avatar
1 vote
0 answers
25 views

Kink in Dispersion Relationship due to Electron Phonon Coupling

How can I start from a Hamiltonian with electron-phonon coupling and show that a kink should show up in the energy dispersion relationship? In a brief communication called "Universal Nodal Fermi ...
Christopher Jacobs's user avatar
1 vote
0 answers
41 views

Phonon eigenfrequencies under time reversal

In G. P. Srivastava's "The Physics of Phonons", 1e., the ansatz which solves Newton's second law in the harmonic approximation is taken to be $$ u_\alpha(\ell b;t) =\frac{1}{\sqrt{m_b}}\...
CW279's user avatar
  • 277
0 votes
0 answers
44 views

Why longitudinal acoustic phonons (LA) do not have a dipole moment?

For a phonon mode to be able to emit electromagnetic radiation, it must have a dipole moment. However, it is not intuitive to me why the LA phonon does not have a dipole moment: suppose all atoms in ...
physstudent11's user avatar
11 votes
1 answer
2k views

Why haven't we found thermal superconductors?

First of all I want to apologize if this is a stupid question. I'm a layman who's merely very interested in physics, without a degree to my name. I was trying to research electric superconductors ...
user3106891's user avatar
1 vote
1 answer
81 views

How to interpret huge number of phonons?

In my condensed matter class we have seen how to treat the problem of vibration in a lattice in quantum mechanics. After heavy calculation we derive that the number of phonons with a given crystal ...
CoolerThanACooler's user avatar
3 votes
2 answers
138 views

How phonon emerges from the quantum mechanics of the lattice?

In all textbooks and lecture notes I've seen so far, a phonon is introduced by imposing the (second) quantization condition on the classical Hamiltonian of the bodies connected with springs. However, ...
Mapleleaf's user avatar
0 votes
0 answers
82 views

Question about Debye's and Einstein's Heat Capacity Theory

I am reading the phonon part of Omar's textbook, but I am a bit confused over the way through which the distribution of the frequencies of oscillators are determined. In Einstein's model all ...
蕭力諶's user avatar
  • 123
10 votes
1 answer
764 views

Are there phonons in air?

Phonons are typically used to describe quantised vibrations in solids. However, is it legitimate to talk about phonons for e.g. a sound wave propagating in air? Contrary to photons that are particles ...
m137's user avatar
  • 1,181
2 votes
0 answers
61 views

Does bubble-phonon-bubble diagram matter for conductivity of electron-phonon system?

In linear response, electrical conductivity due to electron-phonon coupling (EPC) is calculated by using the Kubo formula. Typically, electronic self-energy due to such coupling is included, and such ...
xiaohuamao's user avatar
  • 3,621
0 votes
0 answers
67 views

Born-Oppenheimer approximation in many-body perturbation theory

In order to obtain phonon spectrum, we usually do Born-Oppenheimer approximation and assume that the electrons are always at the ground state when the atoms move, and by calculating the force on each ...
jywu's user avatar
  • 351
0 votes
0 answers
128 views

Acoustic phonons & Debye model, optical phonons & Einstein model

In our class today we spoke about the Einstein and Debye models. We associated the Einstein model with the optical phonons and the Debye one with the acoustic phonons. But I have a question: what is ...
imbAF's user avatar
  • 1,344
0 votes
1 answer
104 views

Calculating the nr. of phonon modes depending on atom nr. in a crystal and dimensions

I am trying to understand how we can determine the correct nr. of phonon modes of a crystal lattice, because I am trying to show that the volume of a state in reciprocal space is $(\frac{2\pi}{L})^3$. ...
imbAF's user avatar
  • 1,344
0 votes
0 answers
62 views

Conceptual understanding of the phonon and its mode

As stated in Wikipedia, the phonon is a quasiparticle, it's the representative of the collective oscillation of the particles which build a crystal. These particles can be atoms, ions etc. The ...
imbAF's user avatar
  • 1,344
0 votes
0 answers
384 views

How to differentiate longitudinal and transverse phonons from the phonon dispersion curve?

I know that there are two kinds of phonons: acoustic and optical. Acoustic phonons have zero frequency at the $\Gamma$ point, whereas optical phonons have a non-zero frequency at the $\Gamma$ point. I ...
Mohamed's user avatar
  • 171
1 vote
0 answers
83 views

Why does Debye model predict that, for big wavelenghts, the relationship between the frequency and the wave number of phonons is linear?

I'm studying Debye model for the specific heat capacity of solids. In class we found first of all that the number of modes per frequency is proportional to the frequency squared. We found that there ...
Fede's user avatar
  • 435
0 votes
0 answers
23 views

In Debye model, If rigid coupling between layers by each atom is exist, the soundwave can be propagated to other layers?

My question is mainly related to (a). What I`m trying to say is that considering the specimen is constructed to layer by layer and each atom on a layer is rigidly coupled with atom of up and down ...
Hottestbeef's user avatar
1 vote
1 answer
83 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 ...
Len's user avatar
  • 163
1 vote
2 answers
472 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 ...
Abe 's user avatar
  • 57
0 votes
0 answers
39 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 ...
Abe 's user avatar
  • 57
2 votes
0 answers
96 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 ...
pajaro gamboa's user avatar
2 votes
2 answers
101 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 ...
slithy_tove's user avatar
1 vote
1 answer
91 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 ...
Aaron Dunbrack's user avatar
1 vote
1 answer
281 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 ...
Lockhart 's user avatar
6 votes
1 answer
321 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 + \...
SCh's user avatar
  • 736

1
2 3 4 5
8