Microscopic theory of Bose–Einstein condensation of magnons at room temperature

Salman, Hayder, Berloff, Natalia G. and Demokritov, Sergej O. (2017) Microscopic theory of Bose–Einstein condensation of magnons at room temperature. In: Universal Themes of Bose-Einstein Condensation. Cambridge University Press. ISBN 9781107085695

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Abstract

A quantised spin wave – magnon – in magnetic films can undergo Bose- Einstein condensation into two energetically degenerate lowest-energy quan- tum states with non-zero wave vectors ±kBEC. This corresponds to two in- terfering condensates forming spontaneously in momentum space. Brillouin Light Scattering studies for a microwave-pumped film with sub-micrometer spatial resolution experimentally confirm the existence of the two wave- functions and show that their interference results in a non-uniform ground state of the condensate with the density oscillating in space. Moreover, fork dislocations in the density fringes provide direct experimental evidence for the formation of pinned half quantum vortices in the magnon condensate. The measured amplitude of the density oscillation implies the formation of a non-symmetric state that corresponds to non equal occupation of two en- ergy minima. We discuss the experimental findings and consider the theory of magnon condensates which includes, to leading order, the contribution from the non-condensed magnons. The e↵ect of the non-condensed magnon cloud is to increase the contrast of the asymmetric state and to bring about the experimental measurements.

Item Type: Book Section
Faculty \ School: Faculty of Science > School of Mathematics
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Depositing User: Pure Connector
Date Deposited: 08 Dec 2016 00:08
Last Modified: 21 May 2020 00:26
URI: https://ueaeprints.uea.ac.uk/id/eprint/61661
DOI:

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