Terahertz-Range Polar Modes in Domain-Engineered BiFeO₃

The dielectric permittivity and properties of electrically active lattice resonances in nanotwinned BiFeO₃ crystals have been studied theoretically using an earlier established interatomic potential. The results suggest that an array of 71° domain walls with about 2–5 nm spacing enhances the static permittivity of BiFeO₃ by more than an order of magnitude. This enhancement is associated with an electrically active excitation, corresponding to a collective vibration of pinned domain walls at a remarkably high frequency of about 0.3 THz.

Dispersion curves calculated for the monodomain [(a), left] and 71° domain wall [(b), right] structure of Fig. 1. The color scale indicates the projection onto the r component of the Last-type mode with the wave vector q along the s direction, with hotter colors marking a bigger participation ratio.

¹Institute of Physics, Czech Academy of Sciences, Na Slovance 2, 182 21 Prague 8, Czech Republic