Heterostrain rules the flat-bands in magic-angle twisted graphene layers

TL;DR

This paper demonstrates that native heterostrain, rather than twist angle, primarily controls the formation of flat bands in magic-angle twisted graphene layers, influencing electronic correlations and experimental outcomes.

Contribution

It reveals that heterostrain dominates over twist in determining flat bands in twisted graphene, supported by STM measurements and analysis of doping and strain effects.

Findings

Heterostrain is the main factor influencing flat bands near the magic angle.

Tip-induced strain can significantly alter electronic properties.

Electronic correlations further normalize flat bands at low doping.

Abstract

The moir\'e of twisted graphene bilayers can generate flat bands in which charge carriers do not posses enough kinetic energy to escape Coulomb interactions with each other leading to the formation of novel strongly correlated electronic states. This exceptionally rich physics relies on the precise arrangement between the layers.We survey published Scanning Tunnelling Microscope (STM) measurements to prove that near the magic angle, native heterostrain, the relative deformations between the layers, dominates twist in determining the flat bands. This is demonstrated at large doping where electronic correlations have a weak effect and where we also show that tip-induced strain can have a strong influence. In the opposite situation of low doping, we find that electronic correlation further normalize the flat bands in a way that strongly depends on experimental details.