In experiments which take a liquid crystal rapidly from the isotropic to the nematic phase, a dense tangle of defects is formed. In nematics, there are, in principle, both line and point defects (“hedgehogs”), but no point defects are observed until the defect network has coarsened appreciably. In this Letter the expected density of point defects is shown to be extremely low, approximately ${10}^{-8\mathrm{}}$ per initially correlated domain, as a result of the topology (specifically, the homology) of the order-parameter space.

• Received 28 February 1995

DOI:https://doi.org/10.1103/PhysRevLett.75.2502