Strain fields in twisted bilayer graphene

Understand

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 as well as localized structural deformations that introduce disorder and strain.
• Here, we introduce Bragg interferometry, based on four-dimensional scanning transmission electron microscopy, to capture atomic displacement fields in twisted bilayer graphene with twist angles < 2{\deg}.
• Nanoscale spatial fluctuations in twist angle and uniaxial heterostrain are statistically evaluated, revealing the prevalence of short-range disorder in this class of materials.