TY - JOUR TI - Topological structural vortices in multiferroic hexagonal manganites DO - https://doi.org/doi:10.7282/T33N257J PY - 2015 AB - This dissertation seeks to understand ferroelectric domains, which can be viewed as networks of topological structural vortices, in a new class of materials called multiferroic hexagonal manganites RMnO3 (h-RMnO3) with R = rare earths, Y, In and Sc. From an experimental standpoint with solid theoretical background, we will briefly introduce improper ferroelectricity and topological defects in general in chapter 1. Then we start our discussion by reviewing the origin of the topological defect (vortex) in multiferroic material (h-RMnO3) and its self-organized domain network, which will act to motivate the work. We will also discuss the origin of self electric poling effect, self-organized criticality (SOC), and a rare phenomenon - vortex core fragmentation in chapter 2. This will be followed by chapter 3 which mainly discusses the manipulation of topological vortex by applying an external shear strain. The force on vortices in h-RMnO3 generated by shear strain is analogous to the Magnus force that moves superfluid vortices in the direction transverse to the superfluid current. Chapter 4 starts with a brief introduction to the Kibble-Zurek Mechanism (KZM), which is the theoretical background of the connection between cosmology and condensed matter physics. It turns out that multiferroic h-RMnO3 is an excellent test bed for KZM through the study of defect formation, emergent continuous symmetry, and Higgs condensation of the disorder field. In the remaining chapter, we extend our scope from the standard vortex to its "dual description" --partially undistorted antipolar (PUA) vortex. Then we will end this dissertation with a summary of the results and future research directions, which actually open a new path to understand the fundamental properties of this new class of materials. KW - Physics and Astronomy KW - Ferroelectricity LA - eng ER -