Ising lines: Natural topological defects within ferroelectric Bloch walls

Phase-field simulations demonstrate that the polarization order-parameter field in the Ginzburg-Landau-Devonshire model of rhombohedral ferroelectric BaTiO₃ allows for an interesting linear defect, stable under simple periodic boundary conditions. This linear defect, here called the Ising line, can be described as an about 2-nm-thick intrinsic paraelectric nanorod acting as a highly mobile borderline between finite portions of Bloch-like domain walls of opposite helicity. These Ising lines play the role of domain boundaries associated with the Ising-to-Bloch domain-wall phase transition. Therefore, the electric field parallel to the Ising line can be used to induce the Ising line motion, which mediates the switching of both polarization and chirality of the Bloch wall without changing the bulk domain polarization. Detailed description of this study can be found in the paper [V. Stepkova et al., arXiv:1504.07200 (2015)].

Fig 1: Ising line defect in rhombohedral BaTiO₃. When circumventing the core of this defect following a closed path (dashed line) around its axis t, the polarization on this path rotates around the [-211] axis, which is perpendicular to t.