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

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.

10 pages, 1 figure

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Cited by in corpus (2)

• Beyond Kitaev physics in strong spin-orbit coupled magnets
• Spin-$S$ Kitaev-Heisenberg model on the honeycomb lattice: A high-order treatment via the many-body coupled cluster method