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arXiv 0901.2797cond-mat.dis-nn
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Cayley树上的无规润湿跃迁:具有两个关联长度指数的无序一级跃迁

Random wetting transition on the Cayley tree : a disordered first-order transition with two correlation length exponents

Cecile Monthus, Thomas Garel

摘要:

我们考虑Cayley树上的随机润湿过渡,即在最左边的键上存在随机能量的情况下Cayley树上的定向聚合物的问题。在纯的情况下,存在一个一阶跃之间的本地化相位和离域相位,与相关长度指数$ν_{pure}=1$。在无序的情况下,我们发现跃迁仍然是一级的,但在临界区存在两个发散的尺度:典型的关联长度随指数$ν_{typ}=1$发散,而平均关联长度随较大的指数$ν_{av}=2$发散,并支配着有限尺寸标度性质.我们描述的关系与以前研究的模型,由相同的“无限无序不动点”。对于本模型,其中序参量是接触密度$θ_L=l_a/L$(定义为接触的数量$l_a$与总长度$L$的比率),“无限无序不动点”的概念意味着给定样品内的$θ_L$的热波动相对于样品到样品的波动在大尺度下变得可忽略。我们的特征的自由能和接触密度的样本的统计。特别是,正是在临界状态下,我们得到的接触密度不是自平均,但仍然分布在样品中的热力学极限,与分布${\cal P}_{T_c}(θ) = 1/(π\sqrt{θ(1-θ)})$。

英文摘要:

We consider the random wetting transition on the Cayley tree, i.e. the problem of a directed polymer on the Cayley tree in the presence of random energies along the left-most bonds. In the pure case, there exists a first-order transition between a localized phase and a delocalized phase, with a correlation length exponent $ν_{pure}=1$. In the disordered case, we find that the transition remains first-order, but that there exists two diverging length scales in the critical region : the typical correlation length diverges with the exponent $ν_{typ}=1$, whereas the averaged correlation length diverges with the bigger exponent $ν_{av}=2$ and governs the finite-size scaling properties. We describe the relations with previously studied models that are governed by the same "Infinite Disorder Fixed Point". For the present model, where the order parameter is the contact density $θ_L=l_a/L$ (defined as the ratio of the number $l_a$ of contacts over the total length $L$), the notion of "infinite disorder fixed point" means that the thermal fluctuations of $θ_L$ within a given sample, become negligeable at large scale with respect to sample-to-sample fluctuations. We characterize the statistics over the samples of the free-energy and of the contact density. In particular, exactly at criticality, we obtain that the contact density is not self-averaging but remains distributed over the samples in the thermodynamic limit, with the distribution ${\cal P}_{T_c}(θ) = 1/(π\sqrt{θ(1-θ)})$.

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