A paper co-signed by LIST in Nature Magazine

Published on 13/10/2017

In the framework of the Materials Research and Technology (MRT) department's activities, a LIST’s researcher, Jorge Íñiguez, is co-author of a paper published in the October 2017 issue of the Nature Materials publication.

Entitled “Phase coexistence and electric-field control of toroidal order in oxide superlattices”, the article serves to combine experiment and theory to reveal and explain the occurrence of complex dipole orders (e.g., vortex lattices) in nano-structures integrating ferroelectric and paraelectric materials.

Such exotic phases are usually deemed exclusive of spin systems, but here it is shown that they can also be obtained in ferroelectric compounds, with the added advantage that electric fields can be used to control them. Moreover the research demonstrates field-induced order-of-magnitude changes in key functional properties, like piezoelectric and nonlinear optical responses, opening perspectives for advanced (multi)functional applications.

ABSTRACT

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 PbTiO3/SrTiO3 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 a1/a2 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.


> For further information, beyond the article’s abstract, visit nature.com.

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