Condensed Matter Journal Club: "Electronic interactions in twisted bilayer graphene from ab initio-derived screening models"

Abstract: Interacting Hamiltonian models within the low-energy subspace of twisted bilayer graphene (TBG) are useful for understanding electronic phases in TBG. The states outside the modeled subspace screen the electronic interactions, and an uncertainty in the strength of this screening currently limits precise modelling. In this talk, I present density functional theory (DFT) and constrained random phase approximation (cRPA) calculations to quantify screening interactions in bilayer graphene. The screened interactions are found to be distance-dependent but otherwise insensitive to sheet geometry such as stacking registry, interlayer distances, and strains. The screening arises from both bilayer graphene and the hexagonal boron nitride that encapsulates it, and strongly persists at least as far as 25 angstroms. Using these results for bilayer graphene, the interactions in TBG are estimated to be on the higher end of the range of previous estimates.