Topological ferroelectric nanostructures induced by mechanical strain in strontium titanate

Ferroelectric materials exhibit novel topological polarization configurations due to geometric confinements originating from the material shapes and interfaces at the nanoscale. In this study, we demonstrate that those nontrivial topological ferroelectric nanostructures can be tailored in paraelectric nanoporous materials by mechanical loads using phase-field modeling. That is, in nanoporous strontium titanate, periodically-arrayed ferroelectric nanostructures in the shape of networks are formed due to strain concentrations by mechanical loads, and topological polarization configurations, such as hierarchical vortices, woven fabrics and nested structures of spiral like Hopf fibration, are stabilized in the structures strongly affected by the pore arrangements. Our work indicates that various ferroelectric nanostructures with novel shapes and topologies can be designed by controlling the pore arrangements and strain conditions in nanoporous SrTiO₃, and thus provides a new pathway to realize novel topological ferroelectric nanostructures, which are essential for future nanodevices.