Responses of spatiotemporal chaos to oscillating forces.

The responses of soft-mode turbulence, a kind of spatiotemporal chaos seen in electroconvection of a nematic liquid crystal, to alternating-current magnetic fields is investigated to uncover the dynamical properties of spatiotemporal chaos. The dynamical responses can be measured by an order parameter, M(p)(t), which indicates ordering in the convective roll pattern induced by the magnetic field. Determined by properties of the liquid crystal in a magnetic field, M(p)(t) oscillates in accordance with the square of the magnetic field.

Quantitative definition of patterns in soft-mode turbulence suppressing the Nambu-Goldstone mode.

Chaotic patterns in electroconvection of homeotropic nematics, soft-mode turbulence (SMT), and the related spatiotemporal chaos (STC) are discussed, and the quantitative definition of the patterns is considered. The order parameter S, obtained directly from the 2D spectra of the patterns, is introduced. The contribution of the Nambu-Goldstone mode and the increase in pattern regularity under the influence of an external magnetic field H are evaluated.

Link of microscopic and macroscopic fields in nematodynamics.

We have found an unusual and unexpected link between micro- (nematic director) and macro- (velocity) fields in nematodynamics, which exhibits itself in extended defects of a new type. In particular, we have shown that black lines (BLs) observed in electroconvection of a homeotropically aligned nematic layer are simultaneously Bloch's domain walls for the director field and lines of zero velocity intersecting a roll pattern for the convection. A detailed experimental study revealing the fine structure of BLs and their point defects is presented.

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.

Order-disorder phase transition in a chaotic system.

For soft-mode turbulence, which is essentially the spatiotemporal chaos caused by the nonlinear interaction between convective modes and Goldstone modes in electroconvection of homeotropic nematics, a type of order-disorder phase transition was revealed, in which a new order parameter was introduced as pattern ordering. We calculated the spatial correlation function and the anisotropy of the convective patterns as a 2D XY system because the convective wave vector could freely rotate in the homeotropic system. We found the hidden order in the chaotic patterns observed beyond the Lifshitz frequency f(L), and a transition from a disordered to a hidden ordered state occurred at the f(L) with the increase of the frequency of the applied voltages.