Rotational polarization nanotopologies in BaTiO₃/SrTiO₃ superlattices

Ferroelectrics are characterized by domain structures as are other ferroics. At the nanoscale though, ferroelectrics may exhibit non-trivial or exotic polarization configurations under proper electrostatic and elastic conditions. These polar states may possess emerging properties not present in the bulk compounds and are promising for technological applications. Here, the observation of rotational polarization topologies at the nanoscale by means of aberration-corrected scanning transmission electron microscopy is reported in BaTiO₃/SrTiO₃ superlattices grown on cubic SrTiO₃(001). The transition from a highly homogeneous polarization state to the formation of rotational nanodomains has been achieved by controlling the superlattice period while maintaining compressive clamping of the superlattice to the cubic SrTiO₃ substrate. The nanodomains revealed in BaTiO₃ prove that its nominal tetragonal structure also allows rotational polar textures.