Symmetry analysis and Monte Carlo study of a frustrated antiferromagnetic planar (XY) model in two dimensions

The antiferromagnetic planar (XY) model on a triangular lattice is investigated using group-theoretical symmetry arguments combined with extensive Monte Carlo simulations and a detailed finite-size-scaling analysis. This approach allows for a systematic exploration of all possible symmetry-breaking transitions and their associated critical behavior. The entire magnetic-field--versus--temperature phase diagram is deduced. A rich class of possible new critical phenomena is obtained, including the introduction of a new multicritical point describing the confluence of the Ising and Kosterlitz-Thouless universality classes. The existence of the critical point is associated with a domain-wall-induced vortex-antivortex--unbinding transition.