Characterization of the vortex-pair interaction law and nonlinear mobility effects

Employing nematic liquid crystals in a homeotropic cell with a photosensitive wall, dissipative Gift Cards vortex pairs are selectively induced by external illumination and the interaction law is characterized for pairs of opposite topological charges.Contrary to the phenomenological fit with a Fo-Ti force inversely proportional to the distance, the data provide evidence that nonlinear mobility effects must be taken into account.The observations lead to a reconciliation of experiments with theory.