# Questions tagged [quasiparticles]

Quasiparticles and Collective Excitations are emergent phenomena that occur when microscopically complicated systems such as solids behave as if they contained different weakly interacting particles in free space. Examples are: electron quasiparticle, hole, exciton, phonon, polariton, magnon, plasmon, polaron.

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### Energy of Quasi-particles in a BCS superconductor

In BCS theory, we are given the energy of the quasi-particles as $E = \sqrt{\varepsilon^2 + \Delta^2}$ in which $\varepsilon = \frac{\hbar^2k^2}{2m} - \mu$, with $\mu$ being the chemical potential. As ...
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### Zero of energy and chemical potential in a superconductor

I am having trouble grasping some concepts related to how energy is measured in a superconductor. In BCS theory, we are given the energy of the quasi-particles as $E = \sqrt{\varepsilon^2 + \Delta^2}$ ...
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### Spinons, Holons and Orbitons? quasiparticles of the electron?

Today I was reading about the electron and about the spin of electrons and understanding why through the Stern-Gerlach experiment, electrons had a "Spin" with a value of +1/2 and -1/2. ...
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### Lifetime of quasiparticles and poles of the propagator

Suppose I have a system that is invariant under both space and time translations. The Lehmann representation of the propagator says that the poles of the propagator are the exact eigenenergies of the ...
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### Is a quasiparticle just an eigenstate of the Hamiltonian?

The description of quasiparticles seems to come in two flavors: Completely qualitatively, where it is simply said that different (quasi-)particles interact to "form" a quasiparticle, or ...
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### Spin of quasiparticle formed by photon in glass

This previous question about the effective mass of a photon traveling through glass has a few answers that say we can think of it as a quasiparticle with an effective mass. Photons are spin-1, but ...
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### Electrons and holes vs. Electrons and positrons

Drawing parallels between electrons and holes in semiconductors, and electrons and positrons in Dirac equation is certainly useful in the context of learning/teaching the quantum field theory methods, ...
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### What are Skyrmion bubbles?

what exactly is the difference between a skyrmion and a skyrmion bubble? Thanks.
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### Intuition and physical meaning of Crystal Momentum and Effective mass of quasi-particles in Solids

I have read various questions related to mine on StackExchange and articles on Wikipedia and some other sources but I still can't get an intuition for the quantities "Crystal Momentum" and "Effective ...
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### Neutrinos, quasiparticles and Majorana fermions

In connection with topological quantum computing I encountered term Majorana fermions. According to Wikipedia these are: A Majorana fermion, also referred to as a Majorana particle, is a fermion ...
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### Are phonons accepted particles by mainstream physicists?

I just encountered the wikipedia article on phonons, which says that these quasiparticles represent vibrations through matter. Wikipedia says that Phonons have negative mass and negative gravity. But ...
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### Where can I learn about a history of holes?

Holes are quasiparticles that were historically brought to explain semiconductor physics with extra benefit of simplifying the counting of electrons.Who gave the first idea and how did it develop ...
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### Is the Andreev-Bashkin effect a beyond-mean-field effect?

I am reading about the Andreev-Bashkin effect, which concerns the current drag from the interaction between two superfluids. Basically, the interaction between two coupled superfluids leads to the ...
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### A mathematical definition of quasi-particle based on second quantization

Is there a mathematical definition of a quasi-particle? So far, from what I see in textbooks, a quasi-particle is that created by the creation operator $d^*$ which was obtained by a Bogoliubov ...
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### Why do we have to introduce quasiparticles in the Fermi liquid theory

Why is it necessary in Fermi liquid theory to introduce quasiparticles? I understand the notion of system where someone can turn on the interactions slowly (i.e., adiabatically), but I do not ...
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### Are there Goldstone bosons in 1D or 2D?

The Mermin-Wagner theorem states that continuous symmetries cannot be spontaneously broken at finite temperature in systems with short-range interactions in dimensions d ≤ 2. And Goldstone bosons ...
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### What is the definition of a bipolaron and a dipolaron?

I wondered about the exact definition of a bipolaron? In particular, if I have an oxygen vacancy in a metal oxide and the 2 excess electrons (when forming a neutral oxygen vacancy) localise on the 2 ...
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### What are dark excitons and how to find them?

I am reading about excitons and I encountered a few times the term "dark exciton" but I have a hard time finding a good definition. I tried to google it but I only find scientific articles where the ...
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### What creates a negative charge in the material?

What creates a negative charge in the material? Is it an electron or a holon? Holons as I understand is a math. But what then creates an electrostatic repulsion? Is it still electron?
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### Is there a quasi-particle corresponding to sound wave in air medium? [duplicate]

I have seen many quasi-particle here in this list. Is there any quasi-particle concept for sound wave in air medium? If it exists, what's the purpose and usefulness of it? If it does not exist, is ...
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### How do electron holes have spin, and how do they interact with "real" particles / vice versa?

So, I thought I had an uneasy truce with quantum mechanics but I read something today which made spotted combat flare up in my mind again. In solid state semiconductor free electrons certainly have ...
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### Microscopic and macroscopic description of spin waves

Hamiltonian Consider the one-dimensional Heisenberg ferromagnet specified by the Hamiltonian $$H = -\frac{|J|}{2}\sum_{i,\delta} \mathbf{S}_i\cdot \mathbf{S}_{i+\delta}.$$ Here $i$ labels the spin ...
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### Can we track phonon's path similarly to how we track electron's path in a bubble chamber?

An answer to a recent question argues that Standard Model's particles like electron are "real" because we can see their tracks in e.g. bubble chamber. So now I wonder: can we track quasiparticles ...
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### What determines if a quasiparticle is a spinon or a vison?

Across topological literature, I've seen references to spinons and visons. In Kitaev's famous "Anyons in an exactly solved model" paper, he mentions that visons are "spinless bosons" whereas spinons ...
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### What is Quasi-particle weight? [closed]

Hi I just heard this phrase from my classmate yesterday, I am wondering whether someone can explain this real quick for me.
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### In what sense are quasiholes and quasiparticles "excitations" in Fractional Quantum Hall (FQH) systems?

In the theory of Fractional Quantum Hall states, one often sees quasi-holes and quasi-electrons (or quasi-particles) being called "excitations" from the ground state initially given by Laughlin (...
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### Why does a phonon obey the Bose statistic?

Could somebody please explain why the phonon must be a Boson (strictly speaking, it must obey the Bose statistic) regardless what it is composed of? (As I have heard, the lattice vibration of both ...
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### Quasiparticle density of states : how to give it a meaning as the quasi particle are interacting?

There is something I don't understand about quasiparticles density of states. I work with the book "Introduction to many body physics" from Coleman. When he introduces the quasiparticle he does the ...
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### Can magnons or phonons exist at zero temperature?

Can in principle, magnons or phonons exist at zero temperature? If not, why? If yes, how?
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### What is the order of magnitude of the energy released in Majorana fermions collision/annihilation?

Majorana fermion experiment It has been observed a quantum state in a one atom thick wire which in a certain energy range behaves like a Majorana fermion. It is a quasiparticle that arises out of the ...
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### Why must the Bogoliubov transform preserve anticommutation relations?

$\mathbf{Background}$: In my research I am studying the Ising model, expressed in terms of Jordan-Wigner fermions:  H = \sum_{j=1}^n(c_j - c_j^\dagger)(c_{j+1} + c_{j+1}^\dagger) + \lambda c_jc_j^\...
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### Why quasiparticles do not decay in finite system in random phase approximation?

I have tried to apply the conventional recipe of calculating electron self-energy part $\Sigma$ in the random phase approximation (RPA) to the case of finite system and obtained $\mathrm{Im}\,\Sigma=0$...
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### Is it possible to create a photon with energy lower than the plasma frequency inside a plasma?

Suppose we have a plasma with corresponding plasma frequency $\omega_{\text{pl}}$. Next, assume that there is some scattering inside the plasma, due to which photons can be created. Is it possible to ...
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### Example of spin chains with finite-lifetime quasi-particles?

Does anyone know a one-dimensional spin model where the low-energy excitations have a finite lifetime? (E.g. in terms of the spectral function $\mathcal S(k, \omega)$ this means one would get a finite ...
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### How to unify these two distinct pictures of spin waves?

For convenience let's focus on an isotropic ferromagnet, $H = -\sum \boldsymbol{S_i \cdot S_j}$. On a classical level we are often given the picture of spin waves as slowly rotating spins, each ...
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### Physical interpretation of a complex potential for a particle in quantum mechanics

In Griffiths' Quantum Mechanics, it is mentioned in a problem that For an unstable particle that spontaneously disintegrates with a lifetime $\tau$, the total probability of finding the particle ...
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In this Wikipedia link, the definition of exciton is given by An exciton is a bound state of an electron and an electron hole which are attracted to each other by the electrostatic Coulomb force. ...