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Microscopic particles called electrons carry the charge currents which underlie the modern electronic devices. A novel technological paradigm based on magnets relies upon spin currents carried by fundamentally different particles - magnons, carrying a quantum of spin. In this paper, we show that interactions lead to a new exotic particle called squeezed-magnon, consisting of a quantum conglomerate of several magnons and, thus, carrying an angular momentum different from the fundamental quantum. To test such a property we suggest to generalize the observation initially made by Schottky in 1918 that the electronic charge can be measured through the current fluctuations. Spin current fluctuations are predicted to carry the information about the squeezed magnons. Hence, the experimentally feasible investigation of the fluctuations of spin current in a spin pumping setup might be the key to reveal the quantum nature of exotic quasiparticles like the squeezed magnon.

Akashdeep Kamra and Wolfgang Belzig
Phys. Rev. Lett. 116, 146601 (2016)