Fig. 5. DW dynamics revealed by first principles–based model calculations.

(A) Atomistic view of YMnO₃ in the (001) plane across the interlocked antiphase boundary and ferroelectric DW. The MnO₅ polyhedra are shaded in purple. The displacements of apical oxygen atoms in the down-domain (left), DW (middle), and up-domain (right) regions are displayed by red, green, and blue arrows, respectively. The trimers are indicated by dashed triangles. The black and white double-headed arrows illustrate the amplitudes and directions of the periodic DW sliding. (B) Ground-state configuration of the three order parameters across the DW obtained by minimizing the model Hamiltonian. (C) Phonon spectral function projected to the Q, φ, and P modes. The ripples are due to the finite size (120 sites) of the supercell. The lower panels in the log scale show the spectral intensity of the low-energy nondispersive branch. (D) Real-space oscillation of δQ, δφ, and δP for a regular dispersive phonon at the terahertz range (top) and the localized DW sliding mode at the gigahertz range (bottom).