Phase transitions in two-dimensional uniformly frustratedXYspin systems

We investigate the nature of phase transitions in a generalized uniformly frustrated square-lattice model with XY spins. The frustration is made to vary by changing the negative bond strength {η}. From ground-state (GS) analysis we find that, below the critical value {η}=(1/3), the GS is ferromagnetic, while for {η}>(1/3), it is doubly degenerate with canted spin configurations. This suggests the existence of an Ising-like transition. This is confirmed by our extensive Monte Carlo simulations. In addition, there is a Kosterlitz-Thouless-like transition at higher temperature for {η}{≠}1. In the fully frustrated case ({η}=1), these two transitions are merged into a single one of dominant Ising character. These conclusions follow from a finite-size-scaling analysis and a visualization of the ordering.