Structural and electronic transformation in low-angle twisted bilayer graphene

TL;DR

This paper uses numerical simulations to reveal a structural transformation in low-angle twisted bilayer graphene, affecting its electronic properties and creating a distinctive charge density pattern observable via STM.

Contribution

It demonstrates a structural transformation driven by interlayer interactions at twist angles below 1.2°, linking moiré pattern changes to electronic behavior.

Findings

Transformation occurs below 1.2° twist angle

Charge density converges to Bernal stacking pattern

Distinct STM signature of solitonic network

Abstract

Experiments on bilayer graphene unveiled a fascinating realization of stacking disorder where triangular domains with well-defined Bernal stacking are delimited by a hexagonal network of strain solitons. Here we show by means of numerical simulations that this is a consequence of a structural transformation of the moir\'{e} pattern inherent of twisted bilayer graphene taking place at twist angles $\theta$ below a crossover angle $\theta^{\star}=1.2^{\circ}$. The transformation is governed by the interplay between the interlayer van der Waals interaction and the in-plane strain field, and is revealed by a change in the functional form of the twist energy density. This transformation unveils an electronic regime characteristic of vanishing twist angles in which the charge density converges, though not uniformly, to that of ideal bilayer graphene with Bernal stacking. On the other hand, the stacking domain boundaries form a distinct charge density pattern that provides the STM signature of the hexagonal solitonic network.