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

Abstract

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 < <math xmlns="http://www.w3.org/1998/Math/MathML"><mn>110</mn></math> > _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.