Propagating electrohydrodynamic instabilities in nematics

Abstract

We show that a propagating electrohydrodynamic instability occurs in a nematic liquid crystal at the threshold of DC excitation if the symmetry of a planar aligned cell is changed by introducing a small pretilt of the director. Flexoelectric torques, which are b.pi/2 out of phase with those produced by other couplings, provide the driving mechanism for the propagating mode, whose direction depends on that of the applied field. Some experimental observations on this mode are also presented.