Space charge and screening in bilayer graphene

TL;DR

This paper investigates how an external charge is screened in undoped bilayer graphene, revealing a unique ground state reconstruction and a linear Thomas-Fermi screening behavior similar to a 2D electron gas.

Contribution

It introduces a detailed analysis of space charge formation and screening in bilayer graphene, highlighting a linear Thomas-Fermi theory applicable at large charge Z.

Findings

Ground state reconstruction involves valence electrons forming a space charge

Screening behavior is described by a linear Thomas-Fermi theory for large Z

Bilayer's dielectric constant matches that of a 2D electron gas in the long-wavelength limit

Abstract

Undoped bilayer graphene is a two-dimensional semimetal with a low-energy excitation spectrum that is parabolic in the momentum. As a result, the screening of an arbitrary external charge $Ze$ is accompanied by a reconstruction of the ground state: valence band electrons (for $Z>0$) are promoted to form a space charge around the charge while the holes leave the physical picture. The outcome is flat neutral object resembling the regular atom except that for $Z \gg 1$ it is described by a strictly linear Thomas-Fermi theory. This theory also predicts that the bilayer's static dielectric constant is the same as that of a two-dimensional electron gas in the long-wavelength limit.