Electronic sound modes and plasmons in hydrodynamic two-dimensional metals

TL;DR

This paper analyzes how sound modes and plasmons behave in hydrodynamic two-dimensional metals, showing that plasmons dominate over traditional sound waves and are robust against hydrodynamic effects, with implications for experiments.

Contribution

It provides an analytical model characterizing the crossover between sound modes and plasmons in 2D Fermi liquids, highlighting the dominance of plasmons in the hydrodynamic regime.

Findings

Plasmons replace zero and first sound in hydrodynamic limit.

Plasmon dispersion remains robust despite hydrodynamic effects.

Implications for experiments in clean 2D electron gases.

Abstract

Using an analytically tractable kinetic model of a two dimensional Fermi liquid of electrons, we characterize the crossovers between zero sound, first sound and plasmons. For experimentally realized Fermi liquids in a hydrodynamic limit, both zero and first sound waves are essentially replaced by plasmons. The plasmon dispersion relation is robust against hydrodynamic effects, up to acquiring the viscous-limited decay rate of a first sound wave in the hydrodynamic limit. We discuss implications for experiments in clean two dimensional electron gases.