Coulomb screening and collective excitations in a graphene bilayer

TL;DR

This paper studies Coulomb screening and collective excitations in graphene bilayers, revealing anisotropic static screening, frequency-dependent dynamic screening, and similarities to Fermi gases in doped systems.

Contribution

It provides new insights into the anisotropic static screening and the transition from Dirac to Fermi gas behavior in graphene bilayers.

Findings

Static screening is anisotropic and stronger in undoped bilayers.

Dynamic screening exhibits Dirac gas behavior at low frequencies and Fermi gas at high frequencies.

Doped graphene bilayers behave similarly to Fermi gases with two energy valleys.

Abstract

We have investigated the Coulomb screening properties and collective excitations in a graphene bilayer. The static screening effect is anisotropic and is much stronger in the undoped graphene bilayer than in a monolayer graphene [1]. The dynamic screening shows the properties of a Dirac gas in the low frequency and that of a Fermi gas in the high frequency. The transition from the Dirac to the Fermi gas is also observed in the plasmon spectrum. Finally, we find that an electron gas in a doped graphene bilayer has quite similar properties as those of a Fermi gas in materials containing two energy valleys.