Questions tagged [collective-excitations]

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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 ...
5
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4answers
260 views

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 ...
4
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1answer
162 views

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 ...
2
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1answer
65 views

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 ...
2
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1answer
141 views

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 $$ ...