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Polar topologies, such as vortex and skyrmion, have attracted significant interest due to their unique physical properties and promising applications in high-density memory devices. To date, all known polar vortices are present in or induced by ferroelectric materials. In this study, we find polar vortex arrays in paraelectric SrTiO3. Using multislice electron ptychography, the evolution of vorticity along the vortex axis is revealed in twisted bilayers of SrTiO3 with deep-sub-angstrom resolution and one picometer accuracy. The surprising finding of polar vortices in a paraelectric crystal opens up opportunities for polarization physics and corresponding new devices. The authors find polar vortex arrays in twisted paraelectric SrTiO3. By employing multislice electron ptychography, the atomic structures of different layers are effectively resolved, allowing for the identification of depth-dependent rotation reversal of the in-plane polarization.
Sha et al. (2024) studied this question.