Symmetry-dependent defect structures in soft-mode turbulence

In the soft-mode turbulence (SMT) in electroconvection of homeotropic nematic systems, which is a kind of spatiotemporal chaos induced by nonlinear interaction between two two-dimensional (2D) XY fields, the Nambu-Goldstone modes, and the convective modes, a curious line structure called blackline has been discovered. We measured the density of the blackline as a function of control parameters, ac voltage, and frequency. By detailed observations and analysis, it is clarified that the blackline is a structure of the nematic director in the x-y plane and includes a sequence of point defects. We discussed similarity with the density of the blackline and that of the point defect in the conventional 2D XY model. The occurrence of this type of defects is only due to the symmetry in the SMT and independent of the properties of fluctuations.