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arXiv 0803.0178cond-mat.stat-mechmath-phmath.MP
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Ginzburg-Landau多项式与临界点和三临界点附近磁化强度的渐近行为

Ginzburg-Landau Polynomials and the Asymptotic Behavior of the Magnetization Near Critical and Tricritical Points

Richard S. Ellis, Jonathan Machta, Peter Tak-Hun Otto

摘要:

由于布卢姆和卡佩尔的一个重要的晶格自旋模型的平均场的版本,我们证明了意想不到的连接之间的渐近行为的磁化强度,相变的结构,和一类多项式,我们称之为金斯堡-朗道多项式。该模型依赖于参数n、beta和K,它们分别表示自旋数、逆温度和相互作用强度。我们的主要工作是研究磁化强度m(beta_n,K_n)对于适当序列(beta_n,K_n)的渐近行为,这些序列(beta_n,K_n)收敛到模型的二阶点或三临界点,并且位于相共存区域的各个子集内。主要结果是:当(beta_n,K_n)收敛于其中一个点(beta,K)时,m(beta_n,K_n)~ c| β-β_n| ^gamma-> 0.在这个公式中,gamma是一个正的常数,c是一个多项式g的唯一正的全局极小点,我们称之为金兹伯格-朗道多项式。该多项式作为适当缩放的自由能泛函的极限而出现,其全局最小值点定义了模型的相变结构。对于所研究的每个序列(beta_n,K_n),相应的Ginzburg-Landau多项式的全局极小点的结构反映了(beta_n,K_n)所经过的区域中自由能泛函的全局极小点的结构,从而反映了该区域中模型的相变结构. Ginzburg-Landau多项式的性质使临界现象的Ginzburg-Landau现象学的预言严格,m(beta_n,K_n)的渐近公式使三临界点的启发式标度理论严格。

英文摘要:

For the mean-field version of an important lattice-spin model due to Blume and Capel, we prove unexpected connections among the asymptotic behavior of the magnetization, the structure of the phase transitions, and a class of polynomials that we call the Ginzburg-Landau polynomials. The model depends on the parameters n, beta, and K, which represent, respectively, the number of spins, the inverse temperature, and the interaction strength. Our main focus is on the asymptotic behavior of the magnetization m(beta_n,K_n) for appropriate sequences (beta_n,K_n) that converge to a second-order point or to the tricritical point of the model and that lie inside various subsets of the phase-coexistence region. The main result states that as (beta_n,K_n) converges to one of these points (beta,K), m(beta_n,K_n) ~ c |beta - beta_n|^gamma --> 0. In this formula gamma is a positive constant, and c is the unique positive, global minimum point of a certain polynomial g that we call the Ginzburg-Landau polynomial. This polynomial arises as a limit of appropriately scaled free-energy functionals, the global minimum points of which define the phase-transition structure of the model. For each sequence (beta_n,K_n) under study, the structure of the global minimum points of the associated Ginzburg-Landau polynomial mirrors the structure of the global minimum points of the free-energy functional in the region through which (beta_n,K_n) passes and thus reflects the phase-transition structure of the model in that region. The properties of the Ginzburg-Landau polynomials make rigorous the predictions of the Ginzburg-Landau phenomenology of critical phenomena, and the asymptotic formula for m(beta_n,K_n) makes rigorous the heuristic scaling theory of the tricritical point.

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