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?
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