Publication: The effects of thermal and correlated noise on magnons in a quantum ferromagnet
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2018-09-18
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IoP publishing ltd
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Abstract
The dynamics and thermal equilibrium of spin waves (magnons) in a quantum ferromagnet as well as the macroscopic magnetisation are investigated. Thermal noise due to an interaction with lattice phonons and the effects of spatial correlations in the noise are considered. We first present a Markovian master equation approach with analytical solutions for any homogeneous spatial correlation function of the noise. We find that spatially correlated noise increases the decay rate of magnons with low wave vectors to their thermal equilibrium, which also leads to a faster decay of the ferromagnet’s magnetisation to its steady-state value. For long correlation lengths and higher temperature we find that additionally there is a component of the magnetisation which decays very slowly, due to a reduced decay rate off astmagnons. This effect could be use ful for fast and noise-protected quantum or classical information transfer and magnonics. We further compare ferromagnetic and antiferromagnetic behaviour in noisy environments and find qualitatively similar behaviour in Ohmic but fundamentally different behaviour in super-Ohmic environments.
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© 2018 The Author(s). We would like to thank Andrew Greentree for helpful discussions and support. This work was supported in part by the Australian Government through the Australian Research Council (ARC) under projects DP140100375, FT110100225 and CE170100026. It was also supported by computational resources provided by the Australian Government through the National Computational Infrastructure National Facility. JJ acknowledges support by the German Bundesministerium für Bildung und Forschung BMBF. AR and MAMD acknowledge the Spanish MINECO grant FIS2015-67411, the CAM research consortium QUITEMAD+ S2013/ICE-2801, and US Army Research Office through grant W911NF-14-1-0103 for partial financial support.