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arXiv 0801.4096cond-mat.stat-mech
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一个普适性类中批判行为的多样性

Diversity of critical behavior within a universality class

Volker Dohm

摘要:

我们研究了空间各向异性对O $(n)$对称各向异性$ϕ^4$晶格模型的体临界行为和有限尺寸临界行为的影响,该模型在$d$维超立方几何中具有周期性边界条件,在$T_c$之上、之处和之下。讨论了体序参数相关函数、体散射强度和几种通用体振幅关系的双尺度因子普适性的缺乏。对于受限系统,采用重整化群理论在固定维$d$下对$2<d<4$进行最小减法。对于立方对称和$n=1$的情况下,我们的微扰方法产生了良好的协议与Monte Carlo(MC)数据的三维伊辛模型在$T_c$的自由能的有限大小的振幅由Mon [物理。{ \bf 54},2671(1985)]。在$T_c$以下,我们发现过剩自由能的标度函数有一个极小值,并预言这个极小值对各向异性参数的依赖性。相对各向异性对自由能的影响预计将显着大于粘结剂累积量。我们的理论与Selke和Shchur的MC模拟发现的二维伊辛模型的铁磁次近邻(NNN)耦合的Binder累积量的非单调依赖性定量一致[J. Phys. { \bf A 38},L739(2005)]。我们的理论还预测了{ \it反铁磁} NNN耦合的小值的非单调依赖性和存在的Lifschitz点在一个较大的值,这种耦合。有限尺度下的非普适各向异性效应满足一种限制普适性。在$T \neq T_c$的大$L$行为的尾部违反了有限尺寸标度和普适性。

英文摘要:

We study spatial anisotropy effects on the bulk and finite-size critical behavior of the O$(n)$ symmetric anisotropic $ϕ^4$ lattice model with periodic boundary conditions in a $d$-dimensional hypercubic geometry above, at and below $T_c$. The absence of two-scale factor universality is discussed for the bulk order-parameter correlation function, the bulk scattering intensity, and for several universal bulk amplitude relations. For the confined system, renormalization-group theory within the minimal subtraction scheme at fixed dimension $d$ for $2<d<4$ is employed. For the case of cubic symmetry and for $n=1$ our perturbation approach yields excellent agreement with the Monte Carlo (MC) data for the finite-size amplitude of the free energy of the three-dimensional Ising model at $T_c$ by Mon [Phys. Rev. Lett. {\bf 54}, 2671 (1985)]. Below $T_c$ a minimum of the scaling function of the excess free energy is found. We predict a measurable dependence of this minimum on the anisotropy parameters. The relative anisotropy effect on the free energy is predicted to be significantly larger than that on the Binder cumulant. Our theory agrees quantitatively with the non-monotonic dependence of the Binder cumulant on the ferromagnetic next-nearest neighbor (NNN) coupling of the two-dimensional Ising model found by MC simulations of Selke and Shchur [J. Phys. {\bf A 38}, L739 (2005)]. Our theory also predicts a non-monotonic dependence for small values of the {\it antiferromagnetic} NNN coupling and the existence of a Lifschitz point at a larger value of this coupling. The nonuniversal anisotropy effects in the finite-size scaling regime are predicted to satisfy a kind of restricted universality. The tails of the large-$L$ behavior at $T \neq T_c$ violate both finite-size scaling and universality.

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