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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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Equation of motion of quantum fluctuations/ quasi particles

I have a question in my mind, that is haunting me for some time now. I am looking for an equation of motion for a quasiparticle. My actual problem is originated in the Gross-Pitaevski model and the ...
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Distribution of states in quasiparticles model and in SYK model

I am currently approaching the SYK model with a little Normal Fermi Liquid background (go easy on me, it's my first time!). I have encountered these slides by Sachdev, where at some point he talks ...
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Bogoliubov de Gennes formalism for rotating systems

I have a question relating to the Bogoliubov de Gennes formalism. I am studying Bose Einstein condensates and I want to calculate the excitation energies of a system in one dimension (a ring with ...
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General expression for fermionic creation operator subspace

This is perhaps a particular case of the question discussed here. Given a fermionic Fock space $H$ of dimension $2^N$, that is, with $N$ fermionic modes, let $H_n$ be the subspace of states with $n$ ...
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How much entanglement does each quasiparticle carry?

The dynamics of entanglement entropy $S$ out of equilibrium can be understood in some regimes from the point of view of the quasiparticle picture: an excited state acts as a source of pairs of ...
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Why sharp resonance corresponds to a particle?

First picture below is from last section of 23th chapter of Feynman's Lectures on physics. I don't understand the red line. This section talks about resonance in nature. It was very interesting and I ...
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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 ...
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Quasiparticle Density of States

In this paper we have the following: The corresponding quasiparticle density is given by the equation $$n_{qp} = 4N_0 \int_\Delta ^\infty dE \frac{E}{\sqrt{E^2 - \Delta^2}} f(E),$$ where $N_0$ is the ...
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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
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Polaron vs Electron energy level

i just started my study in organic semiconductor. I realized to increase conductivity, polarons are formed in the polymer backbone. From what i read due to localised energy state level by polaron that ...
taqiuddin yusri's user avatar
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What exactly are resonances in particle physics?

I am very confused about this, are they an excited state of a particle where an electron is excited to an upper energy level, which seems less likely to be the case since the resonant states of ...
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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 ...
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Quasi-particle distribution in Fermi liquid theory

In Fermi liquid theory, the quasi-particle is well-defined only near the Fermi surface. However, in calculating specific heat and compressibility, we also assume that the quasi-particle obeys the ...
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Simple everyday examples to represent the concept of Quasiparticles - Bubble example

I was sawing a Youtube Video about Quasiparticles (for this topic it doesn't matter which one), but the video host present examples that were very far for being familiar to a wide audience. In my ...
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Understanding the concept of hole in semiconductor physics [duplicate]

I've studied the Kronig–Penney model and learned about the effective mass theory and I know that at the top of the valence band the effective mass of electrons are negative, this is just an ...
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What is the concept of hole in semiconductor physics?

What is a hole? And how should we describe it to study it properly? Many textbooks refer to it as an empty state that carries a positive charge, but how can an empty state carry a positive charge? And ...
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What is a quasi-photon (⁠•⁠ ⁠▽⁠ ⁠•⁠;⁠)?

Regarding the question- Do quasiphotons have mass? Could someone explain to me what a quasi-photon is in layman's terms?
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Is there such a thing as a bare polariton?

When dealing with photons in matter, I have seen it treated in many ways depending on the material, this leads to exciton polaritons (when dealing with electrons and holes), plasmaritons (dealing with ...
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Do quasiphotons have mass?

If I understand correctly, per special relativity, anything that travels at a speed of $c$ must be massless and conversely, anything massless must travel at precisely $c$ in akl reference frame. We ...
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What exactly is the difference between a quasiparticle and composite particle in QFT/particle physics?

I'm specifically thinking about quasiphotons as the superposition of photons and other interacting particles when light is traveling through a medium. I've been told there's a fundamental difference ...
Mikayla Eckel Cifrese's user avatar
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Why is it that, when light travels in a medium, we say it's made of "quasiparticles"?

I get why, in this model, light isn't really "made of" photons, because photons, by definition have zero mass and travel at $c$, whereas these quasiparticles, if I understand correctly, do ...
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The charge of tunneling Bogoliubov quasiparticles

There are some concepts regarding charge and quasiparticles I can't fully reconcile with one another. Commonly in superconducting literature, one will find that a Cooper pair is made out of two ...
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What is a quon?

I have sometimes seen the term 'quon' in quantum physics and I a not sure what does it mean. Most of the time I see it as a synonym of quasi-particle but sometimes in questions like this one: Infinite ...
Mauricio's user avatar
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Free energy of Bogoliubov quasiparticles

When diagonalising the mean-field Hamiltonian in BCS-theory, there is some freedom as to how one defines the Bogoliubov-operators. One convenient choice is to let \begin{align*} \gamma_{\mathbf{k}0}^\...
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How to distinguish between zeroth, second and higher order sounds?

As I understand it, be it liquid helium or phonons in a solid, one can define the second sound, zeroth sound and higher order sounds as quantum mechanical effects where heat propagates as a wave. ...
Mauricio's user avatar
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How do experimentalists measure the exciton binding energy?

The exciton binding energy in semiconductors is determined theoretically by the energetic difference between the fundamental gap and the optical gap or, in other words, as the energetic difference of ...
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Para- and ortho-excitons in solids with spin-orbit coupling

The names para- and ortho-exciton stem from the fact that -- in superficial analogy to para- and ortho-hydrogen -- the wave function that forms the electron-hole bound state can either be a singlet ...
franz's user avatar
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Exciton nomenclature

In many publications on electronic excitations I stumbled across a categorisation of excitons (electron-hole quasi-particles), namely A- and B-excitons. Could someone please explain the difference ...
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Can Fermi liquid be obtained by a canonical transformation?

The basic assumption of the Ferm-liquid theory is the one-to-one correspondence between the states of an interacting Fermi gas to those of a gas of non-interacting quasiparticles. The question is ...
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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 ...
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Bimolecular recombination: How can it be non-radiative for $e$-$p$ pair?

I have understood that the bimolecular recombination of electrons and holes can be radiative when they meet each other, However, I also heard that there are defect sites that can accept electrons and ...
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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 $E = \sqrt{\varepsilon^2 + \Delta^2}$ ...
poopandstuff's user avatar
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Excitation spectrum in BCS theory and mean field theory

I've recently been learning about the BCS theory of superconductivity. An extremely rough idea is as follows: given the interacting BCS Hamiltonian $$ H = \sum_{\vec{k}\sigma} \xi_{\vec{k}} c^{\dagger}...
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Quasiparticle interference experiment - why backscattering is usually dominant?

I am reading Avraham et. al (2018) Quasiparticle Interference Studies of Quantum Materials about quasi-particle interference (QPI) experiments. In the simplest case where they use QPI to study the ...
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What's a typical lifetime for excitons, or biexcitons?

I've read that a typical lifetime for excitons in a semiconductor is 1-10 picoseconds. I believe these are Wannier-Mott excitons. What are typical lifetimes of other kinds of excitons, for example in ...
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Does zero chemical potential implies zero lowest energy level for non-interacting quasiparticle excitations?

Many of the quasiparticle excitations in solids have non-conservative particle numbers. Examples are phonons, magnons, excitons etc. Therefore, as many posts put, the chemical potential should be zero....
an offer can't refuse's user avatar
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What is a 'multi-energy band' superconductor?

From Phys.org: They write that in lab experiments they've found a short-lived "Higgs mode" within iron-based, high-temperature (but still very cold), multi-energy band, unconventional ...
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What is quasineutral in plasma physics?

What is quasineutral gas? In plasma physics, what exactly quasineutral means? In definition of plasma, it is written that plasma is a quasineutral gas of charged and neutral particles which exhibit ...
Garry's user avatar
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6 votes
1 answer
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What would be a simplified explanation of Quasiparticles? [duplicate]

I recently came across a concept in quantum physics called Quasiparticles. They seemed interesting so, I did a little bit of research about them. However, I still don't understand what they are. The ...
Akhilesh Balaji's user avatar
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2 answers
1k views

What does having an imaginary part of potential imply? [duplicate]

In DJ Griffiths' ''Introduction to Quantum Mechanics" to describe an unstable particle that spontaneously disintegrates he assumed an imaginary part in the potential. What does that signify? What ...
Shubham Kumar's user avatar
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The band structure of Weyl Semimetals

Weyl semimetals are topological quantum materials whose low energy excitations emerges as massles Weyl Fermions. They have a band touching point near the Fermi level called Weyl node. What is ...
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11 votes
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Is differentiating particle and quasiparticle meaningless?

The common notion for quasiparticle is that it is only a toolkit to tend emergent phenomena in solid-state physics easily, and it is a different thing from a "real" particle. But what I ...
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Spectral function and bound states in condensed matter

In condensed matter physics (like in QFT) we can use Feynman's diagrams to compute the self-energy. From here we can obtain the spectral function as: $$ A_{\mathbf k} (\omega) = \frac{-\frac{1}{\pi}\...
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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 ...
Masterme's user avatar
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1 answer
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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 ...
MrArsGravis's user avatar
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1 answer
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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 ...
Mike Stay's user avatar
4 votes
3 answers
485 views

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.
IrDa's user avatar
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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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