arXivDaily arXiv每日学术速递 周一至周五更新
arXiv 1304.2134cond-mat.dis-nn
收藏

分形晶格上纯铁磁和随机铁磁伊辛模型的动力学势垒

Dynamical barriers of pure and random ferromagnetic Ising models on fractal lattices

Cecile Monthus, Thomas Garel

摘要:

研究了分支比为$K$且具有分形维数$d_f=(\ln (2K))/\ln 2$的分级金刚石晶格上的纯铁磁和随机铁磁伊辛模型的随机动力学.我们采用实空间重正化过程介绍了我们以前的工作[C。Monthus和T. Garel,J. Stat. P02037(2013)],以研究平衡时间$t_{eq}(L)$作为零温度附近系统尺寸$L$的函数。对于纯Ising模型,我们得到了行为$t_{eq}(L) \sim L^α e^{β2J L^{d_s}} $,其中$d_s=d_f-1$是界面维数,并计算了前因子指数$α$ .对于随机铁磁伊辛模型,我们导出了零温附近动力学势垒$B_{eq}(L) \equiv (\ln t_{eq}/β)$的重整化规则.对于分形维数$d_f=2$,我们得到动力学势垒的尺度为$ B_{eq}(L)= c L+L^{1/2} u$,其中$u$是一个非零均值的高斯随机变量。而非随机项缩放为$L$对应于系统大小的畴壁的创建的能量成本,波动部分缩放为$L^{1/2}$的特征在于系统大小的畴壁创建后的运动的障碍。这个标度对应于动力学指数$ψ=d_s/2$,与[C. Monthus和T. Garel,J.Phys.A41,115002(2008)]。特别是,它是明显不同的液滴指数$θ\simeq 0.299$在静态的随机铁磁体在相同的晶格。

英文摘要:

We consider the stochastic dynamics of the pure and random ferromagnetic Ising model on the hierarchical diamond lattice of branching ratio $K$ with fractal dimension $d_f=(\ln (2K))/\ln 2$. We adapt the Real Space Renormalization procedure introduced in our previous work [C. Monthus and T. Garel, J. Stat. Mech. P02037 (2013)] to study the equilibrium time $t_{eq}(L)$ as a function of the system size $L$ near zero-temperature. For the pure Ising model, we obtain the behavior $t_{eq}(L) \sim L^α e^{β2J L^{d_s}} $ where $d_s=d_f-1$ is the interface dimension, and we compute the prefactor exponent $α$. For the random ferromagnetic Ising model, we derive the renormalization rules for dynamical barriers $B_{eq}(L) \equiv (\ln t_{eq}/β)$ near zero temperature. For the fractal dimension $d_f=2$, we obtain that the dynamical barrier scales as $ B_{eq}(L)= c L+L^{1/2} u$ where $u$ is a Gaussian random variable of non-zero-mean. While the non-random term scaling as $L$ corresponds to the energy-cost of the creation of a system-size domain-wall, the fluctuation part scaling as $L^{1/2}$ characterizes the barriers for the motion of the system-size domain-wall after its creation. This scaling corresponds to the dynamical exponent $ψ=1/2$, in agreement with the conjecture $ψ=d_s/2$ proposed in [C. Monthus and T. Garel, J. Phys. A 41, 115002 (2008)]. In particular, it is clearly different from the droplet exponent $θ\simeq 0.299$ involved in the statics of the random ferromagnet on the same lattice.

机构、总结、中文摘要均由AI分析而来,可能存在错误,请以论文正文为准。

↑