Oblique-roll electrohydrodynamic instability in nematics

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Abstract
A three-dimensional analysis of the electrohydrodynamic instability in a planar-oriented nematic liquid crystal with stress-free boundary conditions shows that for appropriate, realistic parameters of materials like MBBA and PAA the instability sets in for a periodic roll structure that is oblique with respect to the undisturbed director nbhat. By a change in the frequency and/or application of a magnetic field a continuous transition from perpendicular to oblique rolls can be induced. We analyze the mechanism, discuss the possible influence of nonlinearities, and compare with experiments.