Is a surface plasmon an EM wave?

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Discussion Overview

The discussion revolves around the nature of surface plasmons (SPs) and their relationship with electromagnetic (EM) waves, particularly focusing on whether surface plasmon polaritons (SPPs) can be classified as EM waves. The scope includes theoretical concepts and clarifications regarding the coupling of photons with plasmons.

Discussion Character

  • Debate/contested
  • Conceptual clarification

Main Points Raised

  • One participant suggests that surface plasmons are oscillations of electrons induced by incident EM waves and questions the nature of coupling between photons and plasmons.
  • Another participant explains that any EM wave in a medium couples to electronic excitations, affecting the refractive index and energy distribution, and relates this to surface plasmon polaritons.
  • A later reply emphasizes that while SPPs involve coupling with photons, they cannot be considered pure EM waves due to their dependence on the medium for propagation.
  • Another participant agrees that SPPs are not pure electromagnetic waves but notes that this distinction is not widely claimed.

Areas of Agreement / Disagreement

Participants generally agree that surface plasmon polaritons are not pure electromagnetic waves, but there is disagreement on the implications of this classification and the nature of the coupling involved.

Contextual Notes

The discussion highlights the complexity of defining surface plasmons and SPPs, particularly regarding their propagation characteristics and the role of the medium. There are unresolved aspects concerning the precise nature of coupling and the definitions of wave types.

Aziza
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From my understanding, surface plasmons (SPs) are oscillations of electrons caused by incident EM waves. A photon from the EM wave can couple with a plasmon to create a surface plasmon polariton (SPP). Some books/websites use the words SPP and SP interchangeably, so I am confused as to whether they really are the same thing or not. I am not sure what this 'coupling' really is. My friend assures me that SPPs are actually EM waves since they are coupled with photons, but I think they are still just mechanical waves since they cannot propagate through vacuum and are longitudinal, at least to my understanding. Does anyone know what exactly is coupling, and if this really does cause something to act as an EM wave, if the coupling is done with a photon??
 
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Any EM wave propagating in a medium will couple to electronic excitations. These effects are usually subsumed in the refractive index n of the medium. The relative proportion of energy stored in the em field and in the medium varies with frequency and wavenumber. Usually there is only a small range of frequencies, where both mix considerably, the avoided crossing region. In books this is mostly discussed for phonon polaritons, but the principle is the same for surface plasmon polaritons.
See:
http://en.wikipedia.org/wiki/Polariton
 
DrDu said:
Any EM wave propagating in a medium will couple to electronic excitations. These effects are usually subsumed in the refractive index n of the medium. The relative proportion of energy stored in the em field and in the medium varies with frequency and wavenumber. Usually there is only a small range of frequencies, where both mix considerably, the avoided crossing region. In books this is mostly discussed for phonon polaritons, but the principle is the same for surface plasmon polaritons.
See:
http://en.wikipedia.org/wiki/Polariton

but then we cannot call them pure EM waves, correct? because they do need matter through which they can propagate
 
You are right, they are certainly not pure electromagnetic waves. However, nobody claims this.
 

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