Co-revolving topological defects in a nematic liquid crystal.

A patterned surface defect of strength = +1 and its associated disclination lines can decompose into a pair of surface defects and disclination lines of strength = +1/2. For a negative dielectric anisotropy liquid crystal subjected to an applied ac electric field , these half-integer defects are observed to wobble azimuthally for > than some threshold field and, for sufficiently large fields, to co-revolve antipodally around a central point approximately midway between the two defects. This behavior is elucidated experimentally as a function of applied field strength and frequency , where the threshold field for full co-revolution scales as . Concurrently, nematic electrohydrodynamic instabilities were investigated. A complete field frequency "phase diagram" compellingly suggests that the induced fluctuations and eventual co-revolutions of the ordinarily static defects are coupled strongly to-and driven by-the presence of the hydrodynamic instability. The observed behaviour suggests a Lehmann-like mechanism that drives the co-revolution.