Liquid crystals in two dimensions: First-order phase transitions and nonuniversal critical behavior

Liquid crystals in two dimensions undergo a first-order isotropic-to-quasi-nematic transition, provided the particle interactions are sufficiently ``sharp and narrow''. This implies phase coexistence between isotropic and quasi-nematic domains, separated by interfaces. The corresponding line tension is determined, and shown to be very small, giving rise to strong interface fluctuations. When the interactions are no longer ``sharp and narrow'', the transition becomes continuous, with non-universal critical behavior obeying hyperscaling, and approximately resembling the two-dimensional Potts model.