Discrete-Symmetry Breaking and Novel Critical Phenomena in an Antiferromagnetic Planar ($\mathrm{XY}$) Model in Two Dimensions

Landau-Ginzburg-Wilson symmetry analyses and Monte Carlo calculations for the classical antiferromagnetic planar ($\mathrm{XY}$) model on a triangular lattice reveal a wealth of interesting critical phenomena. From this simple model arise a zero-field transition to a state of long-range order, a new mechanism for spin disordering, and a critical point associated with a possible new universality class.