Phase transitions in the fully frustrated triangular XY model

We investigate the phase transitions in the fully frustrated XY model on the triangular lattice via a microcanonical Monte Carlo method. It is found that the system has two separate phase transitions. At the lower temperature, a Kosterlitz-Thouless transition takes place with a larger-than-universal jump in the spin-wave stiffness. At a slightly higher temperature, the system undergoes a second-order chirality-lattice melting transition with exponents 1/nu=1.20(1) and gamma/nu=1.75(2), which are equal to those of the three-state Ports model apart from statistical uncertainty. We also calculate the universal specific heat amplitude ratio A(+)/A(-) and find it to be 1.05(5). This further suggests that the transition is the same universality class as that of the three-state Potts model since the exact value for the three-state Potts model is known to be unity.