Is a surface plasmon an EM wave?

[Aziza]

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??

 

[DrDu]

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

 

[Aziza]

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

 

[DrDu]

You are right, they are certainly not pure electromagnetic waves. However, nobody claims this.