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  • Title: Bose-Einstein condensation in an ultra-hot gas of pumped magnons.
    Author: Serga AA, Tiberkevich VS, Sandweg CW, Vasyuchka VI, Bozhko DA, Chumak AV, Neumann T, Obry B, Melkov GA, Slavin AN, Hillebrands B.
    Journal: Nat Commun; 2014 Mar 11; 5():3452. PubMed ID: 24613901.
    Abstract:
    Bose-Einstein condensation of quasi-particles such as excitons, polaritons, magnons and photons is a fascinating quantum mechanical phenomenon. Unlike the Bose-Einstein condensation of real particles (like atoms), these processes do not require low temperatures, since the high densities of low-energy quasi-particles needed for the condensate to form can be produced via external pumping. Here we demonstrate that such a pumping can create remarkably high effective temperatures in a narrow spectral region of the lowest energy states in a magnon gas, resulting in strikingly unexpected transitional dynamics of Bose-Einstein magnon condensate: the density of the condensate increases immediately after the external magnon flow is switched off and initially decreases if it is switched on again. This behaviour finds explanation in a nonlinear 'evaporative supercooling' mechanism that couples the low-energy magnons overheated by pumping with all the other thermal magnons, removing the excess heat, and allowing Bose-Einstein condensate formation.
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