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arXiv 0910.2218cond-mat.stat-mech
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二维伊辛模型的有限尺寸分析

Finite size analysis of a two-dimensional Ising model within a nonextensive approach

N. Crokidakis, D. O. Soares-Pinto, M. S. Reis, A. M. Souza, R. S. Sarthour, I. S. Oliveira

摘要:

在这项工作中,我们提出了一个彻底的分析相变发生在铁磁二维伊辛模型,只有最近邻相互作用,在Tsallis非广延统计的框架。我们进行了蒙特卡罗模拟正方形晶格的线性尺寸L范围从32到512。Metropolis算法的统计权重根据非广延统计量进行了调整。观察到$q\leq 0.5$的m(T)曲线不连续。然而,我们已经验证了在临界温度下的能量直方图上只有一个峰,表明发生了连续相变。对于$0.5<q\leq 1.0$体系,我们发现了有序相和无序相之间的连续相变,并通过有限尺寸缩放确定了临界指数。我们验证了临界指数$α$、$β$和$γ$依赖于熵指数$q$,在$0.5<q\leq 1.0$范围内,形式为$α(q)=(10 q^{2}-33 q+23)/20$、$β(q)=(2 q-1)/8$和$γ(q)=(q^{2}-q+7)/4$。另一方面,临界指数$ν$不依赖于$q$。这表明违反的标度关系$2 β+γ=d ν$和$α+2 β+γ=2$和非普适性的临界指数沿铁磁前沿。

英文摘要:

In this work we present a thorough analysis of the phase transitions that occur in a ferromagnetic 2D Ising model, with only nearest-neighbors interactions, in the framework of the Tsallis nonextensive statistics. We performed Monte Carlo simulations on square lattices with linear sizes L ranging from 32 up to 512. The statistical weight of the Metropolis algorithm was changed according to the nonextensive statistics. Discontinuities in the m(T) curve are observed for $q\leq 0.5$. However, we have verified only one peak on the energy histograms at the critical temperatures, indicating the occurrence of continuous phase transitions. For the $0.5<q\leq 1.0$ regime, we have found continuous phase transitions between the ordered and the disordered phases, and determined the critical exponents via finite-size scaling. We verified that the critical exponents $α$, $β$ and $γ$ depend on the entropic index $q$ in the range $0.5<q\leq 1.0$ in the form $α(q)=(10 q^{2}-33 q+23)/20$, $β(q)=(2 q-1)/8$ and $γ(q)=(q^{2}-q+7)/4$. On the other hand, the critical exponent $ν$ does not depend on $q$. This suggests a violation of the scaling relations $2 β+γ=d ν$ and $α+2 β+γ=2$ and a nonuniversality of the critical exponents along the ferro-paramagnetic frontier.

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