Pure Chiral Polar Vortex Phase in PbTiO<sub>3</sub>/SrTiO<sub>3</sub> Superlattices with Tunable Circular Dichroism
Sujit Das, Margaret R. McCarter, Fernando Gómez‐Ortiz, Yun‐Long Tang, Zijian Hong, Anirban Ghosh, Padraic Shafer, Pablo García‐Fernández, Javier Junquera, Lane W. Martin, R. Ramesh
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.