%0 Journal Article
%K temperature
%K Electric fields
%K Polarization
%K ferroelectricity
%K Ferroelectric domains
%K Vortex flow
%K Electric-field control
%K First-order phase transitions
%K Oxide superlattices
%K Condensed matter physics
%K Characterization techniques
%K Ferroelectric phasis
%K Nonlinear optical response
%K Superlattice periods
%A A.R Damodaran
%A J.D Clarkson
%A Z Hong
%A H B Liu
%A A.K Yadav
%A C.T Nelson
%A S.-L Hsu
%A M.R McCarter
%A K.-D Park
%A V Kravtsov
%A A Farhan
%A Y Dong
%A Z Cai
%A H Zhou
%A P Aguado-Puente
%A P García-Fernández
%A J Íñiguez
%A J Junquera
%A A Scholl
%A M.B Raschke
%A L.-Q Chen
%A D.D Fong
%A Ramamoorthy Ramesh
%A L.W Martin
%B Nature Materials
%D 2017
%G eng
%I Nature Publishing Group
%P 1003-1009
%R 10.1038/NMAT4951
%T Phase coexistence and electric-field control of toroidal order in oxide superlattices
%V 16
%X Systems that exhibit phase competition, order parameter coexistence, and emergent order parameter topologies constitute a major part of modern condensed-matter physics. Here, by applying a range of characterization techniques, and simulations, we observe that in PbTiO"3/SrTiO"3 superlattices all of these effects can be found. By exploring superlattice period-, temperature- and field-dependent evolution of these structures, we observe several new features. First, it is possible to engineer phase coexistence mediated by a first-order phase transition between an emergent, low-temperature vortex phase with electric toroidal order and a high-temperature ferroelectric a"1/a"2 phase. At room temperature, the coexisting vortex and ferroelectric phases form a mesoscale, fibre-textured hierarchical superstructure. The vortex phase possesses an axial polarization, set by the net polarization of the surrounding ferroelectric domains, such that it possesses a multi-order-parameter state and belongs to a class of gyrotropic electrotoroidal compounds. Finally, application of electric fields to this mixed-phase system permits interconversion between the vortex and the ferroelectric phases concomitant with order-of-magnitude changes in piezoelectric and nonlinear optical responses. Our findings suggest new cross-coupled functionalities. © 2017 Macmillan Publishers Limited, part of Springer Nature. All rights reserved.