Persistence in systems with conserved order parameter

TL;DR

This paper studies the coarsening dynamics and persistence properties of a one-dimensional Ising model with conserved order parameter, deriving scaling laws and comparing with diffusion-limited aggregation models.

Contribution

It generalizes the domain diffusion model to arbitrary diffusion exponents and relates persistence exponents to aggregation processes, providing new analytical and numerical insights.

Findings

Domain density decays as t^{-1/(2- ext{gamma})}

Persistence exponent varies with gamma and differs from DLCA except at gamma=0

Results unify coarsening and aggregation dynamics in one dimension.

Abstract

We consider the low-temperature coarsening dynamics of a one-dimensional Ising ferromagnet with conserved Kawasaki-like dynamics in the domain representation. Domains diffuse with size-dependent diffusion constant, $D(l) \propto l^\gamma$ with $\gamma = -1$. We generalize this model to arbitrary $\gamma$, and derive an expression for the domain density, $N(t) \sim t^{-\phi}$ with $\phi=1/(2-\gamma)$, using a scaling argument. We also investigate numerically the persistence exponent $\theta$ characterizing the power-law decay of the number, $N_p(t)$, of persistent (unflipped) spins at time $t$, and find $N_{p}(t)\sim t^{-\theta}$ where $\theta$ depends on $\gamma$. We show how the results for $\phi$ and $\theta$ are related to similar calculations in diffusion-limited cluster-cluster aggregation (DLCA) where clusters with size-dependent diffusion constant diffuse through an immobile `empty' phase and aggregate irreversibly on impact. Simulations show that, while $\phi$ is the same in both models, $\theta$ is different except for $\gamma=0$. We also investigate models that interpolate between symmetric domain diffusion and DLCA.