Dynamics of defects in electroconvection patterns

¹ Physikalisches Institut, Universität Bayreuth - D-95440 Bayreuth, Germany
² Research Institute for Solid State Physics and Optics H-1525 Budapest, P.O.Box 49, Hungary

Received: 24 April 2001
Accepted: 17 December 2001

Abstract

In homeotropically aligned nematics with negative dielectric anisotropy the electrohydrodynamic instability occurs above a bend Fréedericksz transition. In the presence of a magnetic field parallel to the liquid crystal slab, ordered roll patterns with a well-defined uniform wave vector appear above the onset of convection. By rotating the cell around an axis perpendicular to the slab by a small angle α, one can manipulate the system into a state with wave vector , where is roughly perpendicular to . We have studied experimentally the motion of defects, which then move essentially perpendicular to the rolls. The direction as well as the magnitude of the velocity as a function of agrees with predictions of the weakly nonlinear theory. In particular, we obtain evidence for the nonanalyticity for .