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arXiv · 1601.05057

The free energy of anisotropic quantum spin systems: Functional integral representation

Peter Woelfle·Natalia B Perkins·Yuriy Sizyuk
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Abstract

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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Peter Woelfle, Natalia B Perkins, Yuriy Sizyuk. 2017-02-08. The free energy of anisotropic quantum spin systems: Functional integral representation. https://doi.org/10.1103/physrevb.95.184408

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