# Theory of non-retarded ballistic surface plasma waves in metal films

## TL;DR

This paper develops a comprehensive theory for surface plasma waves in metal films, revealing a universal self-amplification mechanism unaffected by electronic collision rates, with implications for experimental phenomena like Ferrel radiation.

## Contribution

It introduces a novel, universal self-amplification channel for surface plasma waves in metal films, independent of collision rates, and analyzes effects of film thickness and surface roughness.

## Key findings

- Discovery of a universal self-amplification channel for plasma waves
- Independence of amplification properties from electronic collision rate
- Implications for Ferrel radiation and experimental observations

## Abstract

We present a theory of surface plasma waves in metal films with arbitrary electronic collision rate $\tau$. Both \textit{tangential} and \textit{normal} modes are investigated. A universal self-amplification channel for these waves is established as a result of the unique interplay between ballistic electronic motions and boundary effects. The channel is shown to be protected by a general principle and its properties independent of $\tau$. The effects of film thickness and surface roughness are also calculated. Experimental implications, such as Ferrel radiation, are discussed.