Screening and collective modes in gapped bilayer graphene

TL;DR

This paper investigates the static and dynamic screening properties of gapped bilayer graphene using a comprehensive 4-band model, revealing significant qualitative differences from the simplified 2-band approach, especially regarding Kohn anomalies and plasmon modes.

Contribution

The study introduces the 4-band model for bilayer graphene screening, capturing effects like trigonal warping and Kohn anomalies absent in previous 2-band models.

Findings

Presence of Kohn anomalies in static screening with the 4-band model

Distinct plasmon mode characteristics in the 4-band model

Trigonal warping significantly affects screening properties

Abstract

We study the static and dynamic screening of gapped bilayer graphene. Unlike previous works we use the 4-band model instead of the simplified 2-band model. We find that there are important qualitative differences between the dielectric screening function obtained using the 2-band and that obtained using the 4-band model. In particular within the 4-band model in the presence of a band-gap the static screening exhibits Kohn anomalies that are absent within the 2-band model. Moreover, using the 4-band model, we are able to examine the effect of trigonal warping (absent in the 2-band model) on the screening properties of bilayer graphene. We also find that the plasmon modes have qualitatively different character in the 4-band model compared to 2-band results.