Assessing the nature of nanoscale ferroelectric domain walls in lead titanate multilayers

TL;DR

This study combines theoretical and experimental methods to investigate ferroelectric domain walls in PbTiO3/SrTiO3 superlattices, revealing that Bloch components are not always present and highlighting the complex nature of these domain walls.

Contribution

It provides a comprehensive analysis showing that Bloch polarisation in 180° domain walls is sensitive to boundary conditions and may not always occur, challenging previous assumptions.

Findings

No signatures of Bloch components in experimental measurements

Theoretical predictions depend on boundary conditions

Domain wall structure is more complex than previously thought

Abstract

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. Bloch components in the 180{\deg} 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 work, we 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{\deg} domain walls in PbTiO3/SrTiO3 superlattices might be more sensitive to the boundary conditions than initially thought and is not always expected to appear. 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. Our experimental findings, consistent with our theoretical predictions for realistic domain periods, do not reveal any signatures of a Bloch component in the centres of the 180{\deg} domain walls of PbTiO3/SrTiO3 superlattices, suggesting that the precise nature of domain walls in the ultrathin PbTiO3 layers is more intricate than previously thought and deserves further attention.