Half-integer topological defects in liquid crystals (+½ and −½ disclinations) attract and annihilate. The director field n(x,y) has π-periodicity — rotating by π brings you back. This topology allows half-integer winding numbers impossible in polar systems.
Elastic anisotropy K₂/K₁1.00
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Color encodes director angle θ ∈ [0°,180°) using a π-periodic hue wheel. A +½ defect (marked +) looks like a comet head — directors fan around it in a half-turn. A −½ defect (marked −) has a three-pronged star pattern. Opposite charges attract via a logarithmic Coulomb-like potential V ~ −q₁q₂ ln(r). After annihilation, no defects remain and the field relaxes to uniform order.