A 2D ferroelectric vortex pattern in twisted BaTiO3 freestanding layers

Abstract

The wealth of complex polar topologies1–10 recently found in nanoscale ferroelectrics results from a delicate balance between the intrinsic tendency of the materials to develop a homogeneous polarization and the electric and mechanical boundary conditions imposed on them. Ferroelectric–dielectric interfaces are model systems in which polarization curling originates from open circuit-like electric boundary conditions, to avoid the build-up of polarization charges through the formation of fuxclosure11–14 domains that evolve into vortex-like structures at the nanoscale15–17 level. Although ferroelectricity is known to couple strongly with strain (both homogeneous18 and inhomogeneous19,20), the efect of mechanical constraints21 on thin-flm nanoscale ferroelectrics has been comparatively less explored because of the relative paucity of strain patterns that can be implemented experimentally. Here we show that the stacking of freestanding ferroelectric perovskite layers with controlled twist angles provides an opportunity to tailor these topological nanostructures in a way determined by the lateral strain modulation associated with the twisting. Furthermore, we fnd that a peculiar pattern of polarization vortices and antivortices emerges from the fexoelectric coupling of polarization to strain gradients. This fnding provides opportunities to create two-dimensional high-density vortex crystals that would enable us to explore previously unknown physical efects and functionalities.