Abstract
It is well known that stacking domains form in moiré superlattices due to the competition between the interlayer van der Waals forces and intralayer elastic forces, which can be recognized as polar domains due to the local spontaneous polarization in bilayers without centrosymmetry. We propose a theoretical model which captures the effect of an applied electric field on the domain structure. The coupling between the spontaneous polarization and field leads to uneven relaxation of the domains, and a net polarization in the superlattice at nonzero fields, which is sensitive to the moiré period. We show that the dielectric response to the field reduces the stacking energy and leads to softer domains in all bilayers. We then discuss the recent observations of ferroelectricity in the context of our model.
Highlights
Twistronics, the study of layered systems with a relative twist angle or lattice mismatch between the layers, resulting in moiré superlattices, is one of the most exciting new topics in condensed matter physics
We introduce a model of lattice relaxation in a moiré superlattice which includes the effect of an applied field on the bilayer
We can model moiré superlattices at different levels of theory depending on the contributions we include in Eq (1)
Summary
Twistronics, the study of layered systems with a relative twist angle or lattice mismatch between the layers, resulting in moiré superlattices, is one of the most exciting new topics in condensed matter physics. It was predicted about a decade ago that introducing a small relative twist in a layered system such as bilayer graphene could lead to flat electronic bands, and strongly correlated behavior[1,2]. It is known that the domain structures in moiré materials can lead to interesting effects such as the opening of band gaps, and topologically protected states or channels when an electric field is applied[7,8,9,42,43]. Since the interlayer interactions are sensitive to an applied field, it is reasonable to expect that the field would change the delicate balance and affect the resulting domain structure
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