Topological transition to rest in the electrohydrodynamics of nematics

Some nematic liquid crystals undergo electro-convective instabilities if forced by a low-frequency oscillating electric field. When the forcing amplitude is increased, a series of bifurcations occurs, which correspond to increasing disorder and reduction of the size of the electro-convective rolls. At a threshold, a transition to an electrohydrodynamic state characterised by a high density of topological defects occurs. Here, we show that in some nematic mixtures this transition is replaced by a topological transition to rest, that is, the electrohydrodynamics are quenched by the nucleation of a state that is topologically non-equivalent to the initial texture of the nematic.[GRAPHICS]