KINETICS OF AN ORDER-DISORDER PHASE-TRANSITION WITH TOPOLOGICAL DEFECTS

We have investigated the time evolution of a vectorial model C system following a temperature quench from the disordered state into the orde r-disorder coexistence region, with numerical Langevin simulations. Th e system is characterized by a vectorial, nonconserved order parameter coupled to a conserved quantity such as a concentration. Two differen t ordering mechanisms are observed. If the mean concentration c(o) is c(o)>1/2, then the minority phase is the ordered phase and growth is d riven by long-range diffusion. On the other hand, if c(o)<1/2, then it is the disordered phase that is in the minority. In this case, defect s of the order parameter (vortices) are strongly coupled to that of th e position of the disordered phase. Growth takes place primarily via t he diffusion and coalescence of the defects, giving rise to an n = 1/4 growth exponent over a significant time regime.