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arXiv 2106.13151cond-mat.stat-mech
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具有偏置初始条件的Ising类模型的非平衡动力学

Non-equilibrium dynamics in Ising like models with biased initial condition

Reshmi Roy, Parongama Sen

摘要:

研究了类Ising模型中零温Glauber动力学的动力学不动点。平均场计算中不动点的稳定性分析表明,在伊辛模型中存在一个依赖于配位数$z$的指数.对于广义选民模型,相图是根据这项研究。对不同$z$值的格子上的平均场和短程模型的伊辛模型也进行了数值计算。一个相关的研究是退出概率$E(x_0)$的行为,定义为一个配置结束的概率与所有的自旋开始与$x_0$分数的上自旋。一个有趣的结果是$E(x_0) = x_0$在平均场近似时,$z=2$,这是一致的保守磁化系统。对于较大的$z$值,$E(x_0)$在平均场模型和具有最近邻相互作用的伊辛模型中均表现出通常的有限尺寸依赖的非线性行为。对于这样的行为,使用$y = \frac{(x_0 - x_c)}{x_c}L^{1/ν}$作为缩放变量并且$f(y)=\frac{1+\tanh(λy)}{2}$表现为缩放函数来获得$E(x_0)$的数据塌陷。研究了指数和标度因子的普适性。

英文摘要:

We investigate the dynamical fixed points of the zero temperature Glauber dynamics in Ising-like models. The stability analysis of the fixed points in the mean field calculation shows the existence of an exponent that depends on the coordination number $z$ in the Ising model. For the generalised voter model, a phase diagram is obtained based on this study. Numerical results for the Ising model for both the mean field case and short ranged models on lattices with different values of $z$ are also obtained. A related study is the behaviour of the exit probability $E(x_0)$, defined as the probability that a configuration ends up with all spins up starting with $x_0$ fraction of up spins. An interesting result is $E(x_0) = x_0$ in the mean field approximation when $z=2$, which is consistent with the conserved magnetisation in the system. For larger values of $z$, $E(x_0)$ shows the usual finite size dependent non linear behaviour both in the mean field model and in Ising model with nearest neighbour interaction on different two dimensional lattices. For such a behaviour, a data collapse of $E(x_0)$ is obtained using $y = \frac{(x_0 - x_c)}{x_c}L^{1/ν}$ as the scaling variable and $f(y)=\frac{1+\tanh(λy)}{2}$ appears as the scaling function. The universality of the exponent and the scaling factor is investigated.

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