Screening in gated bilayer graphene

TL;DR

This paper models the electronic gap in gated bilayer graphene using a tight-binding approach, revealing how gate voltage and doping influence the gap through screening effects.

Contribution

It derives an equation for the band gap ratio in bilayer graphene considering screening, gate voltage, and doping, highlighting the asymmetrical behavior caused by donors or acceptors.

Findings

Gap is proportional to gate voltage without doping.

Doping causes asymmetrical gap behavior.

Screening constant determines the gap-to-chemical potential ratio.

Abstract

The tight-binding model of a graphene bilayer is used to find the gap between the conduction and valence bands, as a function of both the gate voltage and as the doping by donors or acceptors. The total Hartree energy is minimized and the equation for the gap is obtained. This equation for the ratio of the gap to the chemical potential is determined only by the screening constant. Thus the gap is strictly proportional to the gate voltage or the carrier concentration in the absence of donors or acceptors. In the opposite case, where the donors or acceptors are present, the gap demonstrates the asymmetrical behavior on the electron and hole sides of the gate bias.