# Comment on "Negative Landau damping in bilayer graphene"

## TL;DR

This paper critically examines previous claims of plasmon instabilities in bilayer graphene with electron drift, demonstrating that such instabilities are artifacts caused by calculation errors and emphasizing the importance of physical effects like broken Galilean invariance.

## Contribution

It clarifies that the predicted plasmon instability in bilayer graphene is an artifact and highlights the significance of physical factors like broken Galilean invariance in plasmon behavior.

## Key findings

- The supposed plasmon instability is due to calculation errors.
- Broken Galilean invariance suppresses plasmon instabilities.
- Spatial dispersion of conductivity is crucial for accurate predictions.

## Abstract

In [Phys. Rev. Lett. vol. 119, p. 133901 (2017)] it was argued that two parallel graphene layers in the presence of electron drift support unstable plasmon modes. Here we show that the predicted plasmon instability is an artifact of errors upon evaluation of graphene polarizability in the presence if electron drift. Crucial role of broken Galilean invariance and spatial dispersion of conductivity for suppression of plasmon instabilities is highlighted.