Percolation-like transition in DLA with two species

We introduce a DLA model with two species in order to simulate the growth of alternate clusters. We perform intensive numerical simulations in two dimensions in which the proportions of the two species are varied. A critical point, analogous to a percolation threshold, is found and a new class of critical exponents is obtained for this transition. Within numerical accuracy, the fractal dimension of the clusters is found to be the same as in the usual DLA model, independent of the species concentrations. Possible connections with the growth of two-dimensional ionic crystals are discussed.