Questions tagged [collective-excitations]
17 questions
7
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4 answers
Why does the breaking of a 'continuous' symmetry lead to gapless excitations but not that of a discrete symmetry?
Goldstone theorem, especially in the context of condensed matter physics, can be stated as:
Whenever there is spontaneous breakdown of a continuous global symmetry, the spectrum of the theory contains gapless excitations. However, this is not true…
SRS
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6
votes
1 answer
What is plasmon really? Is it a charge density wave of electron gas or an EM wave that exists across the metal surface?
Sometimes plasmons are defined as collective plasma oscillations of the free electron gas in a metal. Therefore, plasmons must be a periodic modulation of electron charge density in the metal. But sometimes, plasmons are defined as electromagnetic…
Solidification
- 12,736
5
votes
1 answer
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 between both and also give some historical context…
franz
- 627
3
votes
3 answers
How much does quantum uncertainty contribute to the uncertainty of earthquakes?
More abstractly, the topic is: amplification of quantum uncertainty within dynamically unstable systems.
I'd like to have a calculable toy model, e.g. maybe a quantum version of the famous "abelian sandpile model". We would start in a pure state in…
Mitchell Porter
- 13,692
3
votes
0 answers
Goldstone Modes, Galilean Symmetry, and Negative Excitations in Fermi Gas
Considering the centrality of Goldstone quasiparticles in condensed matter theories, I was wondering if the converse of the theorem might also be true: Does the existence of a gapless excitation imply some broken symmetry?
For example, I would…
Deep Blue
- 1,380
3
votes
0 answers
Qualitative difference of excitations in Fermi VS Bose superfluids
Assume that we have an electrically neutral interacting gas (or liquid) of Bose or Fermi particles in a superfluid state.
For simplicity, assume that the particles interact via an assigned central potential (the fact that the particles may have…
Quillo
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2
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How is a vison excitation in a resonating valence bond (RVB) state related to photon of gauge theories?
I am reading Prof. Sachdev's review on quantum phases of matter (link: https://arxiv.org/abs/1203.4565) and I am a bit confused about how the analogy between U(1) photon excitations in QED and vison (plaquette) defects in a $\mathbb{Z2}$ RVB state…
yaprakonder
- 61
2
votes
2 answers
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 exciton-phonon Hamiltonian (that is, the…
slithy_tove
- 384
2
votes
0 answers
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 state with vanishing total spin or a triplet state…
franz
- 627
2
votes
1 answer
Are charged excitation excited states ? - FQHE
I have been reading tong's lectures notes, as well as Prange / Girvin book and Laughlin nobel's lecture. I still can't figure it out.
What is the laughlin ground state off ?
I understand there are neutral excitations that are either bound qp-qh…
Lou
- 71
2
votes
1 answer
Negative curvature of zero sound dispersion
In the theory of a Landau-Fermi liquid, one of the major predictions is the dispersion of zero sound. From the linearized kinetic equation, we know that the dimensionless dispersion $s$ is given by
$$…
Joshuah Heath
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1
vote
0 answers
Excitation energy from the ground state of a quantum Hamiltonian
Consider the Hamiltonian
$$
\hat{H} = \frac{E_C}{2} \hat{k}^2 - E_J f(\hat{\Phi}),
$$
where $\hat{k}$ and $\hat{\Phi}$ are canonically conjugated variables satisfying the commutation relations $[\hat{\Phi}, \hbar\hat{k}] = i\hbar$ and…
Matteo
- 3,261
1
vote
0 answers
Population inversion requirement for multiexcitonic lasing
I am working with optically active nanomaterials (quantum dots, perovskites), that have pretty large exciton binding energies and can form multiexcitonic complexes, e.g. biexcitons, relatively easily. It has been well established that they also…
Vadim
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1
vote
1 answer
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 the fundamental gap and the first exciton peak in…
franz
- 627
1
vote
0 answers
Features of plasmon and surface plasmon polariton
What is the difference between surface plasmon polariton and plasmon in the Hamiltonian? So let's say that I can diagonalize the Hamiltonian of the system I am studying no matter how complicated that is, how do I distinguish a surface plasmon…
Yepman
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