Modified Functional Integral Method for the Heisenberg Model
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概要
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We propose a modified functional integral method for the S=1/2 three dimensional ferromagnetic Heisenberg model based on the Popov and Fedotov theory. The correlation functions expressed by the auxiliary fields are required to satisfy the spin commutation and anticommutation relations. In one-loop approximation for the partition function, obtained results are in exact agreement with the Tyablikov result of the Green function method of the Heisenberg ferromagnet. This result provides a possible explanation of the physical meaning of the Tyablikov decoupling approximation. Furthermore introducing a higher order correction into the unperturbed part of the partition function, we improve the approximation and we obtain thermal quantities. At low temperatures the temperature dependence of the spin-wave energy is in exact agreement with that of Dyson. Compared with Callen's result, for the temperature dependence of the spontaneous magnetization our result is closer to that of Dyson. The Curie temperature and the critical indices agree with those of the molecular field theory of the Heisenberg ferromagnet.
- 社団法人日本物理学会の論文
- 1995-12-15
著者
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Oguchi Akihide
Department Of Physics Faculty Of Science And Technology Science University Of Tokyo
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Oguchi Akihide
Department Of Physics Faculty Of Science And Technology Science University
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Tejima Syougo
Department of Physics, Faculty of Science and Technology, Science University of Tokyo
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Tejima S
Sci. Univ. Tokyo Chiba
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Tejima Syougo
Department Of Physics Faculty Of Science And Technology Science University
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Oguchi Akihide
Department Of Physics Faculty Of Sciece And Technology Science University Of Tokyo
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