Measuring strain fields in moiré superlattices

Atomically thin or two-dimensional (2D) materials can be assembled into bespoke heterostructures to produce some extraordinary physical phenomena. One exciting and relatively recent example is the formation of moiré superlattices from azimuthally misoriented (twisted) layers. These moiré superlattices result in flat bands that lead to an array of correlated electronic phases. However, in these systems, complex strain relaxation can also strongly influence the fragile electronic states of the material. Precise characterization of these materials and their properties is therefore critical to the field's understanding of the behavior of these novel moiré materials (and 2D heterostructures in general).This talk will discuss how spontaneous mechanical deformations (atomic reconstruction) and resultant intralayer strain fields at twisted bilayer graphene and twisted transition metal dichalcogenides have been quantitatively imaged using Bragg interferometry, based on four-dimensional scanning transmission electron microscopy, and the impact of these mechanical deformations and strain fields to the electronic properties of these moiré superlattices.