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Articles
  • Non-equilibrium thermo-field dynamics and some non-equilibrium properties for anti-ferromagnetic spin system interacting with phonon reservoir   [CET 2015]
  • Author(s)
  • Mizuhiko Saeki
  • ABSTRACT
  • The non-equilibrium thermo-field dynamics for the case of a non-bilinear unperturbed Hamiltonian is formulated for an anti-ferromagnetic spin system interacting with a phonon reservoir in the spin-wave approximation, and thus the method of quantum field theory is extended to such an anti-ferromagnetic spin-wave system. The two kinds of quasi-particle operators are introduced, and their forms are derived for the semi-free boson fields. It is shown that the two quasi-particles decay exponentially with the frequencies and life-times which are different from each other, and also that each quasi-particle changes to the other tilde quasi-particle through the spin-phonon interaction. The expectation values of the spin-wave energy and longitudinal magnetization and the dynamic susceptibilities are investigated numerically for an anti-ferromagnetic system of one-dimensional infinite spins interacting with a damped phonon-reservoir, in the region valid for the lowest spin-wave approximation. The processes of the transient responses of the energy expectation value and longitudinal magnetization to the external static magnetic field are displayed for the various values of the temperature and the anisotropy energy. The transverse and longitudinal susceptibilities are displayed for the various values of the temperature and the anisotropy energy. The two-point Green's function of the semi-free boson fields for the anti-ferromagnetic spin-wave system is derived by introducing the thermal quartet notation, and it is given in a form of $4 ¥times 4$ matrix.
  • KEYWORDS
  • Non-equilibrium thermo-field dynamics, non-equilibrium properties, anti-ferromagnetic spin system
  • References

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