Phase Transition of Moiré Edges in Interfacial Ferroelectrics

Moiré superlattices based on twisted van der Waals
(vdW)
heterostructures have recently emerged as platforms exhibiting intriguing
electrical properties. In particular, interfacial ferroelectricity
has been observed in marginally twisted moiré superlattices
that break the inversion symmetry, exhibiting adjacent domains with
opposite polarization. Polarization switching in these systems is
mediated by moiré edge shifts; however, the underlying physical
mechanisms remain poorly understood. In this work, by combining in
situ scanning probe microscopy with theoretical modeling, we reveal
a phase transition of the moiré edge in which its geometry
reversibly transforms from convex to concave, accompanied by the splitting
of a single domain wall into three. This phase transition can be triggered
by localized pressure applied by the probe tip, which induces bending
of the moiré edge and results in local interlayer sliding.
This finding provides a pathway for tuning the electronic properties
of moiré superlattices by engineering the structure and dynamics
of moiré edges.