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.