Twisted Bilayer Graphene: Interlayer Configuration and Magnetotransport Signatures

• Published in: Annalen der Physik Vol. 529; no. 11
• Main Authors: Rode, Johannes C., Smirnov, Dmitri, Belke, Christopher, Schmidt, Hennrik, Haug, Rolf J.
• Format: Journal Article
• Language: English
• Published: Weinheim Wiley Subscription Services, Inc 01.11.2017
• Subjects: Atomic Force Microscope; Atomic structure; Bilayers; Crystallography; Graphene; Interlayers; Lattices; Magnetotransport; Monolayers; Signatures; Singularities; Superlattices; Twisted Bilayer
• ISSN: 0003-3804; 1521-3889
• DOI: 10.1002/andp.201700025

Twisted Bilayer Graphene may be viewed as very first representative of the now booming class of artificially layered 2D materials. Consisting of two sheets from the same structure and atomic composition, its decisive degree of freedom lies in the rotation between crystallographic axes in the individual graphene monolayers. Geometrical consideration finds angle‐dependent Moiré patterns as well as commensurate superlattices of opposite sublattice exchange symmetry. Beyond the approach of rigidly interposed lattices, this review takes focus on the evolving topic of lattice corrugation and distortion in response to spatially varying lattice registry. The experimental approach to twisted bilayers requires a basic control over preparation techniques; important methods are summarized and extended on in the case of bilayers folded from monolayer graphene via AFM nanomachining. Central morphological parameters to the twisted bilayer, rotational mismatch and interlayer separation are studied in a broader base of samples. Finally, experimental evidence for a number of theoretically predicted, controversial electronic scenarios are reviewed; magnetotransport signatures are discussed in terms of Fermi velocity, van Hove singularities and Berry phase and assessed with respect to the underlying experimental conditions, thereby referring back to the initially considered variations in relaxed lattice structure. Twisted bilayer graphene (TBG) consists of a stack of two rotationally misaligned monolayer lattices. This article reviews the current state of the art in preparation, as well as characterization, of TBG. Special focus is directed towards the preparation technique of folding monolayer graphene via Atomic Force Microscope and investigation of the resulting TBG morphology. Different electronic coupling scenarios, as inferred from magnetotransport measurements, are further evaluated under the consideration of superlattice corrugation.