Persistence exponent in superantiferromagnetic quenching

We measure the persistence exponent in a phase separating two-dimensional s pin system with non-conserved dynamics quenched in a region with four coexi sting stripe phases. The system is an Ising model with nearest neighbor, ne xt-to-the-nearest neighbor and plaquette interactions. Due to the particula r nature of the ground states, the order parameter is defined in terms of b locks of spins. Our estimate of the persistence exponent, theta = 0.42, dif fers from those of the two-dimensional Ising and four state Potts models. O ur procedure allows the study of persistence properties also at finite temp erature T: our results are compatible with the hypothesis that theta does n ot depend on T below the critical point. (C) 1999 Published by Elsevier Sci ence B.V. All rights reserved.