Assessing the Nature of Ferroelectric Domain Walls in Lead Titanate Superlattices

The observation of unexpected polarisation textures such as vortices, skyrmions and merons in various oxide heterostructures has challenged the widely accepted picture of ferroelectric domain walls as being Ising-like [1-3]. Bloch components in the 180° domain walls of PbTiO₃ have recently been reported in PbTiO₃/SrTiO₃ superlattices and linked to domain wall chirality. While this opens exciting perspectives, the ubiquitous nature of this Bloch component remains to be further explored.
In this talk, I will present a comprehensive investigation of domain walls in PbTiO₃/SrTiO₃ superlattices, involving a combination of first- and second-principles calculations, phase-field simulations, diffuse scattering calculations, and synchrotron based diffuse x-ray scattering. Our theoretical calculations highlight that the previously predicted Bloch polarisation in the 180° domain walls in PbTiO₃/SrTiO₃ superlattices might be more sensitive to the boundary conditions than initially thought and is not always expected to appear. I will show that by employing diffuse scattering calculations for larger systems we develop a method to probe the complex structure of domain walls in these superlattices via diffuse x-ray scattering measurements. Through this approach, we investigate depolarization-driven ferroelectric polarization rotation at the domain walls.
Finally, I will present our findings and compare them to the expected experimental signatures of Bloch components in the centres of the 180° domain walls of our PbTiO₃/SrTiO₃ superlattices. Our results suggest that the precise nature of domain walls in the ultrathin PbTiO₃ layers is more intricate than previously thought and deserves more attention.

References
[1] Tang et al., Science 348, 547-551 (2015)
[2] Das et al., Nature 568, 368-372 (2019)
[3] Wang et al., Nat. Mater. 19, 881-886 (2020)