# The energy point of view in plasmonics

## TL;DR

This paper presents a physical theorem linking energy flux and density in plasmonic modes, offering insights into phenomena like mode slowing, high wavevector, and negative refraction in metals.

## Contribution

It introduces a theorem connecting energy propagation and mode properties in plasmonics, enhancing understanding of exotic phenomena in metallic nanostructures.

## Key findings

- The theorem relates group velocity to energy flux and density.
- It explains the physical basis of negative permittivity effects.
- Provides insights into slow light and negative refraction in plasmonics.

## Abstract

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, linking the way energy propagates in metals to the properties of guided modes and Bloch modes in a multilayer, provides a unique physical insight in plasmonics. It allows to better understand 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.