Bose–Einstein condensation in an ultra-hot gas of pumped magnons

• Published in: Nature communications Vol. 5; no. 1; p. 3452
• Main Authors: Serga, Alexander A., Tiberkevich, Vasil S., Sandweg, Christian W., Vasyuchka, Vitaliy I., Bozhko, Dmytro A., Chumak, Andrii V., Neumann, Timo, Obry, Björn, Melkov, Gennadii A., Slavin, Andrei N., Hillebrands, Burkard
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group UK 11.03.2014; Nature Publishing Group
• Subjects: 639/766/119/2791; 639/766/25; 639/766/419; Algorithms; Chemical Phenomena; Gases - chemistry; Hot Temperature; Humanities and Social Sciences; Kinetics; Models, Theoretical; multidisciplinary; Phase Transition; Photons; Science; Science (multidisciplinary); Thermodynamics
• ISSN: 2041-1723; 2041-1723
• DOI: 10.1038/ncomms4452

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. In contrast to real atoms, Bose–Einstein condensation of quasi-particles does not require low temperature, but is obtained via external pumping. Here, the authors show an unexpected transitional dynamics of a Bose–Einstein condensate of magnons due to a nonlinear evaporative supercooling mechanism.