PHASE-TRANSITIONS IN 2-DIMENSIONAL FRUSTRATED XY MODEL

We have studied the critcal behavior of two-dimensional frustrated XY model where the frustration is made to vary by changing the ratio eta between ferromagnetic and antiferromagnetic coupling constants. in this model, as in the fully frustrated XY model, two kinds of phase transitions are possible. One is a Kosterlitz-Thouless phase transition due to the continuous U (1) symmetry of spins and the other an Ising-type phase transition due to the discrete Z(2) symmetry of ground states. From a finite-size scaling analysis, we determine the critical exponents associated with the Ising-type phase transition. According to the Monte Carlo simulation results, we find the exponents to be consistent with the pure Ising values if the ratio eta is not equal to one. On the other hand if the eta is equal to one, in which case the model corresponds to the fully frustrated XY model, the exponents are inconsistent with the pure Ising values.