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Interface pinning and slow ordering kinetics on infinitely ramified fractal structures

机译:无限分枝的界面钉扎和慢有序动力学   分形结构

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摘要

We investigate the time dependent Ginzburg-Landau (TDGL) equation for a nonconserved order parameter on an infinitely ramified (deterministic) fractallattice employing two alternative methods: the auxiliary field approach and anumerical method of integration of the equations of evolution. In the firstcase the domain size evolves with time as $L(t)\sim t^{1/d_w}$, where $d_w$ isthe anomalous random walk exponent associated with the fractal and differs fromthe normal value 2, which characterizes all Euclidean lattices. Such a powerlaw growth is identical to the one observed in the study of the spherical modelon the same lattice, but fails to describe the asymptotic behavior of thenumerical solutions of the TDGL equation for a scalar order parameter. In fact,the simulations performed on a two dimensional Sierpinski Carpet indicate that,after an initial stage dominated by a curvature reduction mechanism \`a laAllen-Cahn, the system enters in a regime where the domain walls betweencompeting phases are pinned by lattice defects. The lack of translational invariance determines a rough free energylandscape, the existence of many metastable minima and the suppression of themarginally stable modes, which in translationally invariant systems lead topower law growth and self similar patterns. On fractal structures as thetemperature vanishes the evolution is frozen, since only thermally activatedprocesses can sustain the growth of pinned domains.
机译:我们使用两种替代方法研究无限分叉(确定性)分形上非守恒阶数参数的时间依赖的Ginzburg-Landau(TDGL)方程:辅助场方法和积分方程的数值计算方法。在第一种情况下,域大小随时间变化为$ L(t)\ sim t ^ {1 / d_w} $,其中$ d_w $是与分形相关的异常随机游动指数,不同于正常值2,该值表征了所有欧几里得格子。这样的幂律增长与在相同晶格上对球形模型的研究中观察到的幂律增长相同,但是未能描述标量阶数参数的TDGL方程数值解的渐近行为。实际上,在二维Sierpinski地毯上进行的仿真表明,在由曲率减小机制laAllen-Cahn主导的初始阶段之后,系统进入一种状态,在该状态下,竞争相之间的畴壁被晶格缺陷固定。缺乏平移不变性决定了粗糙的自由能态景观,许多亚稳态极小值的存在以及对边际稳定模态的抑制,这在平移不变系统中导致幂律增长和自相似模式。在分形结构上,随着温度的消失,由于只有热激活过程才能维持固定域的增长,因此其发展被冻结了。

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  • 年度 1998
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  • 正文语种 {"code":"en","name":"English","id":9}
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