M. E. Zhitomirsky, A. L. Chernyshev
We present a theoretical overview of the phenomenon of spontaneous magnon decays in quantum antiferromagnets. An intrinsic zero-temperature damping of magnons in quantum spin systems is a fascinating many-body effect, which recently attracted significant attention in view of its possible observation in the neutron-scattering experiments. We provide an introduction into the theory of magnon interactions and discuss necessary symmetry and kinematic conditions for spontaneous decays. Various parallels with the decays of anharmonic phonons and excitations in superfluid 4He are extensively used. Three principal cases of spontaneous magnon decays are considered: field-induced decays in the Heisenberg antiferromagnets, zero-field decays in the spiral antiferromagnets, and triplon decays in spin liquids. Analytical results are compared with available numerical data and prospective materials for experimental observation of the decay-related effects are briefly discussed.
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http://arxiv.org/abs/1205.5278
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