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Phase coexistence and electric-field control of toroidal order in oxide superlattices.

  • Author(s): Damodaran, AR;
  • Clarkson, JD;
  • Hong, Z;
  • Liu, H;
  • Yadav, AK;
  • Nelson, CT;
  • Hsu, S-L;
  • McCarter, MR;
  • Park, K-D;
  • Kravtsov, V;
  • Farhan, A;
  • Dong, Y;
  • Cai, Z;
  • Zhou, H;
  • Aguado-Puente, P;
  • García-Fernández, P;
  • Íñiguez, J;
  • Junquera, J;
  • Scholl, A;
  • Raschke, MB;
  • Chen, L-Q;
  • Fong, DD;
  • Ramesh, R;
  • Martin, LW
  • et al.

Published Web Location

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.

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