Flicker vortex structures in multiferroic materials

Computer simulation of ferroelastic materials reveals dynamic polar vortex structures related to flexo-electricity between cation and anion lattices. At finite temperatures, the vortices are found to flicker in time and space. Widely spaced ferroelastic twin boundaries nucleate vortices while dense twin boundaries suppress them. The time averaged number of vortices at any site decays exponentially, indicating the highly mobile dynamics of the vortex lattice. Applied electric fields break the rotational symmetry of vortices and finally destroy them. The total number density of vortices follows a field and temperature dependence as N(E)=N0/[1+Aexp(E/k(T-TVF))] with T_VF<0. The observed vortex structures are akin to those observed in magnetic and superconducting disordered vortex lattices.