Molecular-Dynamics Study of a Two-Dimensional FerrodistortiveXYModel with Quartic Anisotropy

We give numerical evidence that in a two-dimensional lattice-dynamical $\mathrm{XY}$ model with quartic anisotropy a conventional continuous phase transition occurs. The formation of clusters in the angular displacement field separated by 90° walls is also demonstrated. Moreover, we give evidence that the critical dynamics of the order-parameter fluctuations is dominated by a central peak which splits at finite wave vectors. This phenomenon is traced back to damped traveling 90° walls.