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

Hayder Salman, Natalia G. Berloff, Sergej O. Demokritov

    Research output: Chapter in Book/Report/Conference proceedingChapterpeer-review

    Abstract

    A quantised spin wave - magnon - in magnetic films can undergo Bose-Einstein condensation (BEC) into two energetically degenerate lowest-energy quantum states with nonzero wave vectors ±kBEC. This corresponds to two interfering condensates forming spontaneously in momentum space. Brillouin Light Scattering studies for a microwave-pumped film with submicrometer spatial resolution experimentally confirm the existence of the two wavefunctions and show that their interference results in a nonuniform 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 nonsymmetric state that corresponds to nonequal occupation of two energy minima. We discuss the experimental findings and consider the theory of magnon condensates, which includes, to leading order, the contribution from the noncondensed magnons. The effect of the noncondensed magnon cloud is to increase the contrast of the asymmetric state and to bring about the experimental measurements.

    Original languageEnglish
    Title of host publicationUniversal Themes of Bose-Einstein Condensation
    PublisherCambridge University Press
    Pages493-504
    Number of pages12
    ISBN (Electronic)9781316084366
    ISBN (Print)9781107085695
    DOIs
    Publication statusPublished - 27 Apr 2017

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