Flat-band projected versus fully atomistic twisted bilayer graphene

TL;DR

This paper evaluates a projection method for magic-angle twisted bilayer graphene, demonstrating its accuracy in reproducing band structures and energies, and introduces new order parameters for analyzing symmetry-breaking phases.

Contribution

It benchmarks a new projection technique against full tight-binding calculations and introduces novel order parameters for symmetry analysis in MATBG.

Findings

Projection method closely matches full tight-binding results.

Flat-band projection is justified by increased band gap.

New order parameters effectively visualize symmetry breaking.

Abstract

We benchmark the recently proposed projection method [Phys. Rev. B 111, 205133 (2025)] for magic-angle twisted bilayer graphene (MATBG) across various symmetry-breaking phases at charge neutrality. The flat-band projected solutions agree well with the full tight-binding, with band structures and total energies differing by only a few meV. The projection to the flat bands is justified, owing to the increased gap to the remote bands in the normal state. Moreover, we employ a novel set of order parameters that allow us to visualize the wave functions locally in real space and quantify the breaking of various symmetries in the correlated phases. These order parameters are suitable for characterizing MATBG and generic honeycomb systems.