Novel ballistic to diffusive crossover in the dynamics of a one dimensional Ising model with variable range of interaction

The idea that the dynamics of a spin is determined by the size of its neighbouring domains was recently introduced (S. Biswas and P. Sen, Phys. Rev. E {\bf 80}, 027101 (2009)) in a Ising spin model (henceforth, referred to as model I). A parameter $p$ is now defined to modify the dynamics such that a spin can sense domain sizes up to $R = pL/2$ in a one dimensional system of size $L$. For the cutoff factor $p$ \to 0$, the dynamics is Ising like and the domains grow with time$t$diffusively as$ t^{1/z}$with$z=2$, while for$p=1$, the original model I showed ballistic dynamics with$z \simeq 1$. For intermediate values of$p$, the domain growth, magnetisation and persistence show model I like behaviour up to a macroscopic crossover time$ t_1 \sim pL/2$. Beyond$t_1$, characteristic power law variations of the dynamic quantities are no longer observed. The total time to reach equilibrium is found to be$t = apL + b(1-p)^3L^2$, from which we conclude that the later time behaviour is diffusive. We also consider the case when a random but quenched value of$p$ is used for each spin for which ballistic behaviour is once again obtained.

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