Hey so the "Surface Plasmon" wikipedia page says

Surface plasmons (SPs) are coherent delocalized electron oscillations that exist at the interface between any two materials where the real part of the dielectric function changes sign across the interface

What the fuck? Changes sign?

The real part of the complex dielectric function (i.e., complex permittivity) just says how charges displace in an electric field. "Reversing the sign" of it implies that charges go one way in one material and the other way in another material. This makes no fucking sense. Charges always go the same direction in an electric field.

Is the wikipedia page just wrong?

  • DialecticalShaman [none/use name]
    ·
    3 years ago

    Seems like it should be:

    Surface plasmons (SPs) are coherent delocalized electron oscillations that exist at the interface between any two materials where the real part of the dielectric function electric susceptibility changes sign across the interface.

    The example they give is air vs. metal. Which matches up with the poor and good conductors on the materials chart in the article for Permittivity. For those materials permittivity goes from epsilon_r <<1 to >>1 and susceptibility is epsilon_r -1.

    • ass [he/him,comrade/them]
      ·
      3 years ago

      Yes!!

      Fuck I spent so long confused by such a simple error. I actually realized it a few seconds ago when i was reading a textbook and it defined electric susceptibility.

      • DialecticalShaman [none/use name]
        ·
        3 years ago

        I can't edit it right now, but someone should get on that.

        I think it should be changed to this:

        '''Surface plasmons''' ('''SPs''') are coherent [[delocalized electron]] oscillations that exist at the interface between any two materials where the real part of the [[Electric Susceptibility|electric susceptibility]] changes sign across the interface (e.g. a metal-dielectric interface, such as a metal sheet in air). SPs have lower energy than bulk (or volume) [[plasmon]]s which quantise the longitudinal electron oscillations about positive ion cores within the bulk of an [[Fermi gas|electron gas]] (or plasma).

        • ass [he/him,comrade/them]
          ·
          3 years ago

          i've never edited wikipedia before and i don't have an account, but if it's still not fixed after my exam in a few days i'll fix it

        • ass [he/him,comrade/them]
          ·
          3 years ago

          Actually i think it is correct how it is written now, just extremely confusing. i saw the same phrasing in the textbook.

          When they say the sign changes across the interface, i think this is just a confusing way of saying the two sides are out of phase so at a given instant in time the vertical E fields will point in opposite directions on either side of the interface. It's confusing to me because i'm pretty sure the phase delay results from the complex component, not the real component, but maybe I just haven't looked at the math enough to grasp some important nuance