Ab-initio analysis of superstructures revealed by STM on bilayer graphene

TL;DR

This study uses density functional theory to analyze twisted bilayer graphene, reproducing experimental STM superstructures and providing evidence for their electronic origin, especially over AA stacking regions.

Contribution

It offers the first ab-initio STM simulation of twisted bilayer graphene superstructures, confirming their electronic origin and correlation with stacking regions.

Findings

STM images reproduce superstructures and corrugations observed experimentally.

Superstructure maxima occur over AA stacking regions.

Electronic effects are confirmed as the origin of superstructures.

Abstract

In this work we performed density functional theory calculations for a twisted bilayer graphene (BLG). Several conmensurable rotation angles were analyzed and for each one a constant height mode STM image was obtained. These STM images, calculated under the Tersoff-Hamman theory, reproduce the main features experimentally observed, paticularly superstructures and giant corrugations. In this way we confirm that STM characterization of twisted BLG can produce superstructures whose tunneling current intensity maxima occur over regions with $AA$ stacking. Additionally we give new evidence in favour of an electronic origin for the superstructures instead another physical grounds.