A constrained Potts antiferromagnet model with an interface representation

We define a 4-state Potts model ensemble on the square lattice, with the constraints that neighbouring spins must have different values, and that no plaquette may contain all four states. The spin configurations may be mapped into those of a two-dimensional interface in a 2 + 5 dimensional space. If this interface is in a Gaussian rough phase (as is the case for most other models with such a mapping) then the spin correlations are critical and their exponents can be related to the stiffness governing the interface fluctuations. Results of our Monte Carlo simulations show height fluctuations with an anomalous dependence on the wavevector, intermediate between the behaviours expected in a rough and in a smooth phase; we argue that the smooth phase (which would imply long-range spin order) is the best interpretation.