Domain Topology and Domain Switching Kinetics in a Hybrid Improper Ferroelectric

TL;DR

This paper uncovers the complex domain topology and switching kinetics in hybrid improper ferroelectrics, revealing a rich variety of domain structures, topological features, and reversible boundary behaviors that influence charged domain wall formation.

Contribution

It introduces a detailed domain topology model in hybrid improper ferroelectrics, highlighting Z4xZ2 domain structures, Z3 vortices, and zipper-like antiphase boundaries affecting switching behavior.

Findings

Identification of Z4xZ2 domain structure with Z3 vortices.

Reversible creation and annihilation of domain walls at antiphase boundaries.

Rich topological features influencing charged domain wall abundance.

Abstract

Charged polar interfaces such as charged ferroelectric domain walls or heterostructured interfaces of ZnO/(Zn,Mg)O and LaAlO3/SrTiO3, across which the normal component of electric polarization changes suddenly, can host large two-dimensional conduction. Charged ferroelectric walls, which are energetically unfavorable in general, were found to be mysteriously abundant in hybrid improper ferroelectric (Ca,Sr)3Ti2O7 crystals. From the exploration of antiphase boundaries in bilayer-perovskites, we discover that each of four polarization-direction states is degenerated with two antiphase domains, and these eight structural variants form a Z4xZ2 domain structure with Z3 vortices and five distinct types of domain walls, whose topology is directly relevant to the presence of abundant charged walls. We also discover a zipper-like nature of antiphase boundaries; they are the reversible creation/annihilation centers of pairs of two types of ferroelectric walls (and also Z3-vortex pairs) in 90 and 180 degree polarization switching. Our results demonstrate the unexpectedly rich nature of hybrid improper ferroelectricity.