Nonequilibrium phase transition by directed Potts particles

We introduce an interface model with q-fold symmetry to study the nonequilibrium phase transition (NPT) from an active to an inactive state at the bottom layer. In the model, q different species of particles are deposited or are evaporated according to a dynamic rule, which includes the interaction between neighboring particles within the same layer. The NPT is classified according to the number of species q. For q=1 and 2, the NPT is characterized by directed percolation, and the directed Ising class, respectively. For $q \ge 3$, the NPT occurs at finite critical probability p_c, and appears to be independent of q; the $q=\infty$ case is related to the Edwards-Wilkinson interface dynamics.