Questions tagged [collective-excitations]

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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 ...
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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 ...
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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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Symmetry of momentum distribution in trapped BEC

Is the momentum distribution of excitations in a BEC symmetric? Even if there is a step potential (which I think should not make a difference because this is in real space)? I think yes, because ...
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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 ...
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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 ...
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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 ...
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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 ...
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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 ...
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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 $$ ...
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