各向异性量子自旋系统的自由能：泛函积分表示
The free energy of anisotropic quantum spin systems: Functional integral representation
摘要：
本文提出了一种计算各向异性量子自旋系统自由能的方法。我们利用Hubbard-Stratonovich变换将一般双线性超交换哈密顿量的配分函数表示为经典含时场上的泛函积分。在一般情况下，结果被表示为无穷级数。该系列可以在伊辛型模型的情况下总结。对于任何有序态，我们导出了高斯自旋涨落对自由能贡献的简洁表达式。
英文摘要：
In this work, we propose a method for calculating the free energy of anisotropic quantum spin systems. We use the Hubbard-Stratonovich transformation to express the partition function of a generic bilinear super-exchange Hamiltonian in terms of a functional integral over classical time-dependent fields. In the general case the result is presented as an infinite series. The series may be summed up in the case of Ising-type models. For any ordered state we derive a compact expression for the contribution of Gaussian spin fluctuations to the free energy.
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