Stacking transition in bilayer graphene caused by thermally activated rotation

TL;DR

This paper reports a thermally activated transition in bilayer graphene from a twisted to AB stacking, driven by van der Waals interactions and self-cleaning, with associated topological and pseudospin changes.

Contribution

It reveals a novel thermally induced self-rotation mechanism causing stacking transition in bilayer graphene, linked to microscopic adsorbent unpinning.

Findings

Transition from twisted to AB stacking observed

Topological and pseudospin changes accompany the transition

Transition driven by van der Waals energy and self-cleaning

Abstract

Crystallographic alignment between two-dimensional crystals in van der Waals heterostructures brought a number of profound physical phenomena, including observation of Hofstadter butterfly and topological currents, and promising novel applications, such as resonant tunnelling transistors. Here, by probing the electronic density of states in graphene using graphene-hexagonal boron nitride tunnelling transistors, we demonstrate a structural transition of bilayer graphene from incommensurate twisted stacking state into a commensurate AB stacking due to a macroscopic graphene self-rotation. This structural transition is accompanied by a topological transition in the reciprocal space and by pseudospin texturing. The stacking transition is driven by van der Waals interaction energy of the two graphene layers and is thermally activated by unpinning the microscopic chemical adsorbents which are then removed by the self-cleaning of graphene.