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Strain fields in twisted bilayer graphene

Journal Article · · Nature Materials
 [1];  [2];  [3];  [3];  [4];  [3];  [3];  [5];  [5];  [6]
  1. Univ. of California, Berkeley, CA (United States); Calvin Univ., Grand Rapids, MI (United States)
  2. Univ. of California, Berkeley, CA (United States)
  3. Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States)
  4. Brown Univ., Providence, RI (United States)
  5. National Institute of Materials Science, Namiki, Tsukuba (Japan)
  6. Univ. of California, Berkeley, CA (United States); Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States); Canadian institute for Advanced Research, Toronto (Canada)

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.

Research Organization:
Lawrence Berkeley National Laboratory (LBNL), Berkeley, CA (United States)
Sponsoring Organization:
Office of Naval Research Young Investigator Program; National Science Foundation (NSF); USDOE
OSTI ID:
1818271
Journal Information:
Nature Materials, Journal Name: Nature Materials Journal Issue: 7 Vol. 20; ISSN 1476-1122
Publisher:
Springer Nature - Nature Publishing GroupCopyright Statement
Country of Publication:
United States
Language:
English

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Cited By (2)

Tunable large Berry dipole in strained twisted bilayer graphene journal May 2021
Moiré Commensurability and the Quantum Anomalous Hall Effect in Twisted Bilayer Graphene on Hexagonal Boron Nitride text January 2020