Research master thesis: Second-Principles Modelling of Polar Topologies in the Prototypical Ferroelectric BaTiO3

Abstract

With recent breakthroughs in the observation of topological textures in polarization, several ferro- electric materials have garnered attention for hosting these exotic phases. Materials with a Bloch nature are particularly sought after for this purpose. Despite decades of research into it, only re- cently have non-trivial topological textures been observed or realized in Barium Titanate (BaTiO3). These swirling polarization textures present interesting physics and have far reaching applications, particularly with information storage. In this thesis we explore possible textures that can be realized in bulk BaTiO3 and we extend on prior studies and predict the realization of topological phases new to this prototypical ferroelectric. We then study the evolution of these phases with respect to temperature and external electric fields, to see the extent to which these textures are preserved and the associated transitions that occur from strong enough perturbations. The studies are performed using second-principles methods and a developed model potential for Barium Titanate. Notably we extend an observed lattice of vortices and anti-vortices and demostrate that the texture undergoes a topological phase transformation and conforms to a lattice of merons and antimerons in bulk BaTiO3. We then identify and further study a metastable skyrmionic phase previously unreported in Barium Titanate and explore how stable the phase is with respect to external fields. We also study the local strains in the structures to explore if it could provide prospects for experimental realization.