The energy point of view in plasmonics

The group velocity of a plasmonic guided mode can be written as the ratio of the flux of the Poynting to the integral of the energy density along the profile of the mode. This theorem, which links the way in which energy propagates in metals to the properties of guided modes and Bloch modes in a multilayer, provides a unique physical insight into plasmonics. It allows better understanding of the link between the negative permittivity of metals and the wide diversity of exotic phenomenon that occur in plasmonics—like the slowing down of guided modes, the high wavevector, and the negative refraction.