Polar Skyrmions in Layers of Ferroelectric Perovskite Superlattice

Superlattice of ferroelectric perovskite material (PbTiO₃)_n/(SrTiO₃)_n hosts exotic topological structures such as polar skyrmion bubbles at room temperature [1]. Despite the absence of antisymmetric exchange interaction, stabilization of these non-collinear polarization structures is intriguing. We identify [2] that the electrostriction energy term, which couples electric polarization vector and elastic strain, is responsible for any possible non-collinear structure. An application of electric field may then stabilize skyrmion structures. We have formulated [2] the coupled Euler equations of the polarization vector and the elastic displacement vector and have found skyrmion solution with unique topological number in each layer of the superlattice for a range of electric fields. The types of skyrmions vary from Neel to Bloch depending upon the position of the layer inside the bubble structure, as reported in the experiments [1].

[1] S. Das et al., Nature 568, 368 (2019).

[2] S. Sen and S. S. Mandal, arXiv:2409.16100 .