An accurate description of the structural and electronic properties of twisted bilayer graphene-boron nitride heterostructures

TL;DR

This paper investigates how hBN substrates influence the electronic properties of twisted bilayer graphene using atomistic models and relaxation effects, revealing significant substrate-induced modifications and potential ways to recover degeneracy.

Contribution

The study introduces an atomistic tight-binding approach combined with molecular dynamics to analyze substrate effects on TBG, advancing beyond continuum models.

Findings

hBN substrate induces a large mass gap in TBG

substrate causes strong pseudomagnetic fields and breaks layer degeneracy

degeneracy can be restored with a second hBN layer

Abstract

Twisted bilayer graphene (TBG) has taken the spotlight in the condensed matter community since the discovery of correlated phases at the so-called magic angle. Interestingly, the role of a substrate on the electronic properties of TBG has not been completely elucidated. Up to now, most of the theoretical works carried out in order to understand this effect have been done using continuum models. In this work, we have gone one step ahead and have studied heterostructures of TBG and hBN using an atomistic tight-binding model together with semi-classical molecular dynamics to take into account relaxation effects. We found that the presence of the hBN substrate has significant effects to the band structure of TBG even in the case where TBG and hBN are not aligned. Specifically, the substrate induces a large mass gap and strong pseudomagnetic fields which break the layer degeneracy. Interestingly, such degeneracy can be recovered with a second hBN layer. Finally, we have also developed a continuum model that describes the tight-binding band structure. Our results show that a real-space tight-binding model in combination with semi-classical molecular dynamics are a powerful tool to study the electronic properties of supermoir\'e systems and that using this real-space methodology could be key in order to explain certain experimental results in which the effect of the substrate plays an important role.