%0 Journal Article
%J Nature Communications
%D 2018
%T Configurable topological textures in strain graded ferroelectric nanoplates
%A K.-E. Kim
%A S. Jeong
%A K. Chu
%A J.H. Lee
%A G.-Y. Kim
%A F. Xue
%A T.Y. Koo
%A L.-Q. Chen
%A S.-Y. Choi
%A Ramamoorthy Ramesh
%A C.-H. Yang
%K Article
%K bismuth
%K chirality
%K destruction
%K discrete element method
%K electrical property
%K ferrite
%K leisure
%K memory
%K microscopy
%K piezoelectricity
%K vorticity
%X Topological defects in matter behave collectively to form highly non-trivial structures called topological textures that are characterised by conserved quantities such as the winding number. Here we show that an epitaxial ferroelectric square nanoplate of bismuth ferrite subjected to a large strain gradient (as much as 105 m-1) associated with misfit strain relaxation enables five discrete levels for the ferroelectric topological invariant of the entire system because of its peculiar radial quadrant domain texture and its inherent domain wall chirality. The total winding number of the topological texture can be configured from - 1 to 3 by selective non-local electric switching of the quadrant domains. By using angle-resolved piezoresponse force microscopy in conjunction with local winding number analysis, we directly identify the existence of vortices and anti-vortices, observe pair creation and annihilation and manipulate the net number of vortices. Our findings offer a useful concept for multi-level topological defect memory. © 2018 The Author(s).
%B Nature Communications
%I Nature Publishing Group
%V 9
%G eng
%R 10.1038/s41467-017-02813-5
%0 Journal Article
%J Nano Letters
%D 2017
%T Stability of Polar Vortex Lattice in Ferroelectric Superlattices
%A Z. Hong
%A A.R. Damodaran
%A F. Xue
%A S.-L. Hsu
%A J. Britson
%A A.K. Yadav
%A C.T. Nelson
%A J.-J. Wang
%A J.F. Scott
%A L.W. Martin
%A Ramamoorthy Ramesh
%A L.-Q. Chen
%K Article
%K competition
%K Crystal lattices
%K Ferroelectric superlattice
%K ferroelectricity
%K Geometric length
%K Neodymium compounds
%K Phase-field simulation
%K Polar vortex
%K Polarization
%K simulation
%K Superconducting materials
%K Topological structure
%K Topology
%K Vortex flow
%X A novel mesoscale state comprising of an ordered polar vortex lattice has been demonstrated in ferroelectric superlattices of PbTiO3/SrTiO3. Here, we employ phase-field simulations, analytical theory, and experimental observations to evaluate thermodynamic conditions and geometric length scales that are critical for the formation of such exotic vortex states. We show that the stability of these vortex lattices involves an intimate competition between long-range electrostatic, long-range elastic, and short-range polarization gradient-related interactions leading to both an upper and a lower bound to the length scale at which these states can be observed. We found that the critical length is related to the intrinsic domain wall width, which could serve as a simple intuitive design rule for the discovery of novel ultrafine topological structures in ferroic systems. © 2017 American Chemical Society.
%B Nano Letters
%I American Chemical Society
%V 17
%P 2246-2252
%G eng
%R 10.1021/acs.nanolett.6b04875