Energy-lowering and constant-energy spin flips: Emergence of the percolating cluster in the kinetic Ising model

TL;DR

This study investigates the microscopic mechanisms controlling the emergence of percolating clusters in the kinetic 2D Ising model after a quench, highlighting the role of constant-energy spin flips in the timing of percolation phenomena.

Contribution

It reveals how constant-energy spin flips influence the timescales of percolation cluster formation and stabilization in the kinetic Ising model, providing insights applicable to similar non-conserved order parameter systems.

Findings

Constant-energy flips control the stabilization time of percolating clusters.

Cluster size heterogeneity and domain size are independent of flip probability before percolation.

Stabilization time scales as the inverse of the flip probability for small p.

Abstract

After a sudden quench from the disordered high-temperature $T_0\to\infty$ phase to a final temperature below the critical point $T_F \ll T_c$, the non-conserved order parameter dynamics of the two-dimensional ferromagnetic Ising model on a square lattice (2dIM) initially approaches the critical percolation state before entering the coarsening regime. This approach involves two timescales associated with the first appearance (at time $t_{{\rm p}_1}>0$) and stabilization (at time $t_{\rm p}>t_{{\rm p}_1}$) of a giant percolation cluster, as previously reported. However, the microscopic mechanisms that control such timescales are not yet fully understood. In this paper, in order to study their role on each time regime after the quench ($T_F=0$), we distinguish between spin flips that decrease the total energy of the system from those that keep it constant, the latter being parametrized by the probability $p$. We show that the cluster size heterogeneity $H(t,p)$ and the typical domain size $\ell (t,p)$ have no dependence on $p$ in the first time regime up to $t_{{\rm p}_1}$. On the other hand, the time for stabilizing a percolating cluster is controlled by the acceptance probability of constant-energy flips: $t_{\rm p}(p) \sim p^{-1}$ for $p\ll 1$ (at $p=0$, the dynamics gets stuck in a metastable state). These flips are also the relevant ones in the later coarsening regime where dynamical scaling takes place. Because the phenomenology on the approach to the percolation point seems to be shared by many 2d systems with a non-conserved order parameter dynamics (and certain cases of conserved ones as well), our results may suggest a simple and effective way to set, through the dynamics itself, $t_{{\rm p}_1}$ and $t_{\rm p}$ in such systems.