Phase diagram of generalized fully frustrated XY model in two dimensions

It is shown that the phase diagram of the two-dimensional generalized fully frustrated XY model on a square lattice contains a crossing of the chirality transition and the Kosterlitz-Thouless (KT) transition, as well as a stable phase characterized by a finite helicity modulus Υ and an unbroken chirality symmetry. The crossing point itself is consistent with a critical point without any jump in Υ , with the size (L) scaling Υ∼L^-0.63 and the critical index ν≈0.77 . The KT transition line remains continuous beyond the crossing but eventually turns into a first-order line. The results are established using Monte Carlo simulations of the staggered magnetization, helicity modulus, and the fourth-order helicity modulus.