Periodic polar vortices in BaTiO3/SrTiO3 superlattices monolithically grown on silicon.

Polar textures in ferroelectric superlattices have been so far reported almost exclusively in PbTiO3-based systems and predominantly on oxide substrates. Owing to their nanometer-scale dimensions and emergent functionalities, whirling topological polar textures would be especially compelling when realized on silicon with Complementary-Metal-Oxide-Semiconductor-compatible materials. Here, we demonstrate the stabilization of vortex tubes in BaTiO3/SrTiO3 superlattices epitaxially grown on silicon. The vortices in each BaTiO3 layer order along the < 110 > BaTiO3 crystallographic directions, forming an in-plane 90-degree stripe pattern. This polar configuration represents the ground state of the system as shown by phase field modelling and further validated by temperature dependent X-ray diffraction. Phase field modelling shows a strong dependence of the domain morphology on the strain and highlights the elastic and electrostatic coupling of the BaTiO3 and SrTiO3 layers. Our findings expand the materials and substrate platforms known to host polar topological textures, opening new opportunities for integrating complex ferroelectric states with silicon-based technologies.