Strain fields in twisted bilayer graphene

Van der Waals heteroepitaxy allows deterministic control over lattice mismatch or azimuthal orientation between atomic layers to produce long-wavelength superlattices. The resulting electronic phases depend critically on the superlattice periodicity and localized structural deformations that introdu...

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Bibliographic Details
Published in:Nature materials Vol. 20; no. 7; pp. 956 - 963
Main Authors: Kazmierczak, Nathanael P., Van Winkle, Madeline, Ophus, Colin, Bustillo, Karen C., Carr, Stephen, Brown, Hamish G., Ciston, Jim, Taniguchi, Takashi, Watanabe, Kenji, Bediako, D. Kwabena
Format: Journal Article
Language:English
Published: London Nature Publishing Group UK 01.07.2021
Nature Publishing Group
Springer Nature - Nature Publishing Group
Subjects:
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Bilayers
Biomaterials
Chemistry and Materials Science
Condensed Matter Physics
electronic properties and devices
electronic properties and materials
Graphene
Heterostructures
Interferometry
Lattice vibration
MATERIALS SCIENCE
Mathematical analysis
mechanical and structural properties and devices
Mechanics (physics)
Nanotechnology
Optical and Electronic Materials
Reconstruction
Saddle points
Strain
Superlattices
Tensors
transmission electron microscopy
two dimensional materials
ISSN:1476-1122, 1476-4660, 1476-4660
Online Access:Get full text
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Summary:Van der Waals heteroepitaxy allows deterministic control over lattice mismatch or azimuthal orientation between atomic layers to produce long-wavelength superlattices. The resulting electronic phases depend critically on the superlattice periodicity and localized structural deformations that introduce disorder and strain. In this study we used Bragg interferometry to capture atomic displacement fields in twisted bilayer graphene with twist angles <2°. Nanoscale spatial fluctuations in twist angle and uniaxial heterostrain were statistically evaluated, revealing the prevalence of short-range disorder in moiré heterostructures. By quantitatively mapping strain tensor fields, we uncovered two regimes of structural relaxation and disentangled the electronic contributions of constituent rotation modes. Further, we found that applied heterostrain accumulates anisotropically in saddle-point regions, generating distinctive striped strain phases. Our results establish the reconstruction mechanics underpinning the twist-angle-dependent electronic behaviour of twisted bilayer graphene and provide a framework for directly visualizing structural relaxation, disorder and strain in moiré materials. Complete strain tensor fields of twisted bilayer graphene are quantitatively mapped, revealing two-regime reconstruction mechanics depending on twist angle.
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USDOE
AC02-05CH1123; N00014-19-1-2199; OIA-1921199
National Science Foundation (NSF)
Office of Naval Research Young Investigator Program
ISSN:1476-1122
1476-4660
1476-4660
DOI:10.1038/s41563-021-00973-w