Phase diagram of ferromagnetic XY model with nematic coupling on a triangular lattice

The phase diagram of a ferromagnetic XY model with a nematic coupling (coupling strength x) on a triangular lattice is studied by means of Monte Carlo simulation. The algebraic-magnetic order associated with Kosterlitz-Thouless (KT) transition is observed over the whole x range. In the large x region, the phase transition from the algebraic-magnetic order to the algebraic-nematic order occurs at TI. In addition, this phase transition can be scaled with the two-dimensional Ising critical exponents, demonstrating that the present system belongs to the universality class of Ising transition at TI.