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arXiv 2001.01693cond-mat.stat-mech
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一维伊辛模型的磁化率:T = 0处的奇点是本质奇点吗?

Susceptibility of the one-dimensional Ising model: is the singularity at T = 0 an essential one?

James H. Taylor

摘要:

零场等温磁化率的一维伊辛模型与最近邻相互作用和有限数量的自旋被证明有一个相对简单的奇异性的温度接近零,只成比例的倒数温度。这是在整个文献中看到的无限链:一个基本的奇点,包括指数依赖于逆温度。假设任意(但有限)数量的自旋和保留条款,通常被认为是在热力学极限下可解的,分析只涉及简单的级数展开,从磁场中闭链的配分函数开始,使用转移矩阵方法获得;或从零场磁化率的表达式通过波动耗散定理发现。在这两种情况下,指数奇点都被完全消除了。此外,每个自旋的磁化率被发现增加与自旋的数量(除了在非相互作用的自旋的情况下),这也是在方差与通常报告的无限链的结果。

英文摘要:

The zero-field isothermal susceptibility of the one-dimensional Ising model with nearest-neighbor interactions and a finite number of spins is shown to have a relatively simple singularity as the temperature approaches zero, proportional only to the inverse temperature. This is in contrast to what is seen throughout the literature for the inifinite chain: an essential singularity that includes an exponential dependence on the inverse temperature. Assuming an arbitrary (but finite) number of spins and retaining terms that are usually considered ignorable in the thermodynamic limit, the analysis involves nothing beyond straightforward series expansions, starting either from the partition function for a closed chain in a magnetic field, obtained using the transfer-matrix approach; or from the expression for the zero-field susceptibility found via the fluctuation-dissipation theorem. In both cases, the exponential singularity is exactly removed. In addition, the susceptibility per spin is found to increase with the number of spins (except in the case of noninteracting spins), a result which is also at variance with what is normally reported for an infinite chain.

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