Critical behavior of the two-dimensional uniformly frustrated charged Coulomb gas

The nature of the phase transition for the two-dimensional Coulomb gas on the square lattice in the presence of a uniform frustration f is studied by Monte Carlo simulation. We present evidence for a nonuniversal Kosterlitz-Thouless (KT) jump for the inverse dielectric constant ε₀^-1 for f=(1/2, (1/3, and (1/4. For the fully frustrated case f=(1/2, two distinct transitions, one KT-like and the other Ising-like, is observed in contrast to earlier studies for the XY model, which suggested only one transition, even though both models are believed to be in the same universality class.