Creating polar antivortex in PbTiO3/SrTiO3 superlattice

Abstract

Nontrivial topological structures offer a rich playground in condensed matters and promise alternative device configurations for post-Moore electronics. While recently a number of polar topologies have been discovered in confined ferroelectric PbTiO3 within artificially engineered PbTiO3/SrTiO3 superlattices, little attention was paid to possible topological polar structures in SrTiO3. Here we successfully create previously unrealized polar antivortices within the SrTiO3 of PbTiO3/SrTiO3 superlattices, accomplished by carefully engineering their thicknesses guided by phase-field simulation. Field- and thermal-induced Kosterlitz–Thouless-like topological phase transitions have also been demonstrated, and it was discovered that the driving force for antivortex formation is electrostatic instead of elastic. This work completes an important missing link in polar topologies, expands the reaches of topological structures, and offers insight into searching and manipulating polar textures.

Engineering polar vortex from topologically trivial domain architecture

“…Unlike their ferromagnetic counterpart, ferroelectrics usually exhibit strong anisotropy that favors particular polar axes, and polarization rotation rarely occurs 5 . As a result, vast majority of polar structures naturally emerging in a ferroelectric are topologically trivial, and nontrivial polar topologies such as closure-domain 6 , 7 , vortex 8 , 9 , skyrmion 10 , meron 11 , and vortex-antivortex pair 12 have only recently been observed in reduced dimensions. It is now understood that in nanostructures such as nanodisks 13 , nanorods 14 , nanodots 15 , nanoislands 16 – 20 , and nanoplates 21 , electrostatic force dominates polar crystalline anisotropy, forcing polarization rotation and thus the formation of vortex.…”

“…With the emergence of big data and ever increasing power consumption in microelectronics, nontrivial polar topologies become attractive as they promise alternative device configurations for high-density data storage 25 as well as ultralow power negative capacitance field effect transistors 26 – 29 . From an application point of view, it is highly desirable if we can engineer nontrivial polar topologies from the ordinary ferroelectrics with topologically trivial domain architecture, and with better understanding on the energetics of polar topologies 12 , 22 , we are now in a position to explore such possibilities. Using a combination of techniques for polarization mapping 30 , atomic imaging 6 , 7 , and three-dimensional reciprocal space mapping (3D-RSM) 31 supported by phase-field simulations 32 , we demonstrate the feasibility of engineering nontrivial polar topologies from topologically trivial domain architecture, and offer a realistic strategy to accomplish it.…”

Phase‐Field Simulations of Tunable Polar Topologies in Lead‐Free Ferroelectric/Paraelectric Multilayers with Ultrahigh Energy‐Storage Performance

“…Notably, PE STO layers also exhibit considerable polarization (up to 0.3 C m −2 ) owing to the strain and internal field. [ 15,18 ]…”

“…The recent discovery of polar topologies in stacked FE multilayers suggests new possibilities for domain engineering and opportunities to further improve the energy performance. The elegant interplay of elastic, electric, and gradient energy enabled by elastic and electric boundary conditions has revealed flux‐closure domains in PbTiO 3 /SrTiO 3 (PTO/STO) multilayers; [ 14,15 ] polar vortices, [ 16,17 ] antivortices, [ 18 ] skyrmions, [ 19 ] and waves [ 20 ] in PTO/STO superlattices; and polar merons [ 21 ] in strained PTO. These FE films with topological polar arrays have intricate polarization structures and rich domain configurations in which a large proportion of the domain walls consist of nonequilibrium polarization states; the polar vortex lattice, e.g., contains continuously rotating dipoles surrounded by tetragonal ( T ) domains.…”

Ferroelectric/paraelectric superlattices for energy storage

“…The observed dipole structures can be deemed antipolar, and hence these systems are good candidates to display antiferroelectric-like behaviour. These superlattices have attracted attention lately since they have been found to host negative capacitance 30 , non-trivial dipole topologies 29,31,32 , and subterahertz collective dynamics 33 , with possible applications for voltage amplification and in electric-field-driven data processing, among others.…”