Two Phase Transitions in the Fully Frustrated<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mi mathvariant="italic">XY</mml:mi></mml:math>Model

Abstract

The fully frustrated $\mathrm{XY}$ model on a square lattice is studied by means of Monte Carlo simulations. A Kosterlitz-Thouless transition is found at ${T}_{\mathrm{KT}}\ensuremath{\approx}0.446$, followed by an ordinary Ising transition at a slightly higher temperature, ${T}_{c}\ensuremath{\approx}0.452$. The non-Ising exponents reported by others are explained as a failure of finite-size scaling due to the screening length associated with the nearby Kosterlitz-Thouless transition.