Transient mode selections in soft-mode turbulence by controlling the Nambu-Goldstone modes

We have studied the soft-mode turbulence (SMT), a type of spatiotemporal chaos observed in the electroconvection of the homeotropic nematic liquid crystals, induced by nonlinear interaction between the long-wave length Nambu-Goldstone modes and the short-wave length convective modes. By applying an external magnetic field H, the NG mode can be controlled and as a result an ordered pattern may be observed. Transiently it is achieved by the dynamical changes of the many domains consisting of regular rolls. Removing the magnetic field, then, the ordered state relaxes to its original SMT pattern. The transient dynamics of such a relaxation process is also investigated. An order parameter called as M _p is used as a quantitative indicator for the transient process. We reveal two regimes of relaxation process: regime I and regime II correspond to the superposition of the modes and the free rotation of wavevector q(r) of the electroconvective pattern, respectively.