Pure Chiral Polar Vortex Phase in PbTiO₃/SrTiO₃ Superlattices with Tunable Circular Dichroism

Abstract

Nontrivial polarization textures have been demonstrated in ferroelectric/dielectric superlattices, where the electrostatic, elastic, and different gradient energies compete in a delicate balance. When PbTiO 3 /SrTiO 3 superlattices are grown on DyScO 3 , the coexistence of ferroelectric domains and vortex structure is observed for n = 12−20 unit cells. Here, we report an approach to achieve single-phase vortex structures in superlattices by controlling the epitaxial strain using Sr 1.04 Al 0.12 Ga 0.35 Ta 0.50 O 3 substrates. The domain width follows Kittel's law with the thickness of the ferroelectric PbTiO 3 layers. A phase transition from vortex to a disordered phase with temperature is characterized by the correlation length. Resonant soft X-ray diffraction circular dichroism at the titanium L-edge reveals enhanced chirality with the thickness of the ferroelectric layer. These results are supported by second-principles simulations, which demonstrate that the integrated helicity increases with n. The stabilization of chiral single-phase polar vortices in ferroelectric/dielectric superlattices can enable novel optoelectronic devices with enhanced ferroelectric−light interaction.