Pure Chiral Polar Vortex Phase in PbTiO<sub>3</sub>/SrTiO<sub>3</sub> Superlattices with Tunable Circular Dichroism.
basic_science · Level V
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- Record sourced from PubMed, PMID 37449842.
- Also identified by DOI 10.1021/acs.nanolett.3c01744.
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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<sub>3</sub>/SrTiO<sub>3</sub> superlattices are grown on DyScO<sub>3</sub>, the coexistence of ferroelectric domains and vortex structure is observed for <i>n</i> = 12-20 unit cells. Here, we report an approach to achieve single-phase vortex structures in superlattices by controlling the epitaxial strain using Sr<sub>1.04</sub>Al<sub>0.12</sub>Ga<sub>0.35</sub>Ta<sub>0.50</sub>O<sub>3</sub> substrates. The domain width follows Kittel's law with the thickness of the ferroelectric PbTiO<sub>3</sub> 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 <i>L</i>-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 <i>n</i>. The stabilization of chiral single-phase polar vortices in ferroelectric/dielectric superlattices can enable novel optoelectronic devices with enhanced ferroelectric-light interaction.