We prove the existence of long-range order for the 3-state Potts antiferromagnet at low temperature on Z d for sufficiently large d. In particular, we show the existence of six extremal and ergodic infinite-volume Gibbs measures, which exhibit spontaneous magnetization in the sense that vertices in one bipartition class have a much higher probability to be in one state than in either of the other two states. This settles the high-dimensional case of the Kotecký conjecture.
IntroductionThe q-state Potts model is a classical model in statistical mechanics, which generalizes the Ising model by allowing more than two states. A special case was first considered by Ashkin and Teller in 1943 [1], while the general model was proposed by Domb and published by Potts in 1951 [38]. Since the late 1970's, the model has drawn substantial attention from mathematicians and physicists alike, largely because it proved to be very rich, displaying a much wider spectrum of phenomena than the simpler Ising model. For an extensive survey of classical results on the Potts model, see Wu [46].While the ferromagnetic regime of the model is by now relatively well understood, the picture for the antiferromagnetic regime is far from complete. Here we consider the 3-state antiferromagnetic (AF) Potts model on the integer lattice Z d . The model assigns a random value f (v) ∈ {0, 1, 2} to each vertex v in some domain Λ ⊂ Z d , favoring different states on adjacent vertices. The probability of any given configuration f is proportional to exp(−βH f ), where β ≥ 0 is a real parameter andwhere the sum is taken over all pairs of nearest neighbors. In other words, f is distributed according to the Boltzmann distribution with the Hamiltonian H f at inverse temperature β.At infinite temperature (β = 0), the values assigned to different vertices are independent, and the model is completely disordered. The Dobrushin uniqueness condition [8] guarantees that, in any dimension, disorder persists at sufficiently high temperature (small β). A fundamental question is whether at low temperature (large β) the model remains disordered or, instead, undergoes a phase transition into an ordered phase. In the latter case, it is also desirable to understand the structure of a typical ordered configuration. Such a phase transition does not occur in every dimension (e.g., for d = 1), and it is interesting to determine in which dimensions (if any) it does.Following an earlier debate in the physical community (see e.g.[2] where a continuous transition was conjectured), Kotecký conjectured circa 1985 (implied in [29], also mentioned in [18]) that in high dimensions, possibly already in three dimensions, the 3-state AF Potts model indeed undergoes a phase transition, and that at sufficiently low temperature, a configuration typically follows one of six patterns. To understand the nature of these patterns, note first that the graph Z d is bipartite, and that each bipartition class forms a sublattice. In a typical large-volume disordered configuration, Thus, µ τ Λ,∞ is the u...