Screening and collective modes in gapped bilayer graphene

We study the static and dynamic screening of gapped AB-stacked bilayer graphene. Unlike previous works we use the full 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 simplified 2-band model and 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 simplified 2-band model. Moreover, using the 4-band model, we examine the effect of trigonal warping on the screening properties of bilayer graphene. We also find that the plasmon modes have a qualitatively different character in the 4-band model compared to the ones obtained using the simplified 2-band model.