Plasmons are the Quanta associated with longitudinal waves propagating in matter through the collective motion of large numbers of electrons. Surface plasmons are a subset of these 'eigen-modes' of the electrons, which are bound to regions in the material where the optical properties reverse, i.e. the interface between a dielectric and conducting medium. However in the low k-vector limit these surface modes couple with the free EM field to yield a polariton type excitation. For more information see www.qub.ac.uk

a collection of electrons that oscillate at a certain frequency

a collective effect within the solid, which may be viewed as a distribution of positive ions and electrons

A flourlike food preparation made from skim milk, and consisting essentially of the unaltered proteid of milk. It is also used in making biscuits and crackers, for mixing with cocoa, etc. A mixture of this with butter, water, and salt is called Plasmon butter, and resembles clotted cream in appearance.