Flexoelectric origin of oblique-roll electrohydrodynamic instability in nematics

We develop the theory of electrohydrodynamic instability in nematic liquid crystals by incorporating the flexoelectric terms. Using a one-dimensional linear analysis of the problem for an applied DC field, we demonstrate that for the usual materials the rolls have an oblique orientation as has been found experimentally. We also provide an experimental evidence for the strong flexoelectric influence on the director profile in the rolls.