Yusuke Nishida, Yasuyuki Kato, Cristian D. Batista
Physics is said to be universal when it emerges regardless of microscopic details. A prominent example is the Efimov effect, i.e., emergence of an infinite tower of three-body bound states obeying discrete scale invariance. Because of its universality and peculiarity, the Efimov effect has been subject to extensive research in chemical, atomic, and nuclear physics for decades. Here we show that collective excitations in Heisenberg magnets (magnons) also exhibit the Efimov effect by tuning an easy-axis exchange or single-ion anisotropy. We locate an anisotropy-induced two-magnon resonance, compute binding energies of three magnons, and find that they fit into the universal scaling law. We propose several approaches to experimentally realize the Efimov effect in quantum magnets and the emergent Efimov states of magnons can be observed with previously-used spectroscopic measurements. Our study thus opens up new avenues for universal few-body physics in solid state systems.
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http://arxiv.org/abs/1208.6214
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