title: Bose-Einstein condensation in an ultra-hot gas of pumped magnons.
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.
authors.affiliation: Fachbereich Physik and Landesforschungszentrum OPTIMAS, Technische Universität Kaiserslautern, 67663 Kaiserslautern, Germany.
authors.forename: Alexander A
authors.initials: AA
authors.lastname: Serga
authors.affiliation: Department of Physics, Oakland University, Rochester, Michigan 48309, USA.
authors.forename: Vasil S
authors.initials: VS
authors.lastname: Tiberkevich
authors.affiliation: Fachbereich Physik and Landesforschungszentrum OPTIMAS, Technische Universität Kaiserslautern, 67663 Kaiserslautern, Germany.
authors.forename: Christian W
authors.initials: CW
authors.lastname: Sandweg
authors.affiliation: Fachbereich Physik and Landesforschungszentrum OPTIMAS, Technische Universität Kaiserslautern, 67663 Kaiserslautern, Germany.
authors.forename: Vitaliy I
authors.initials: VI
authors.lastname: Vasyuchka
authors.affiliation: 1] Fachbereich Physik and Landesforschungszentrum OPTIMAS, Technische Universität Kaiserslautern, 67663 Kaiserslautern, Germany [2] Faculty of Radiophysics, Taras Shevchenko National University of Kyiv, 01601 Kyiv, Ukraine.
authors.forename: Dmytro A
authors.initials: DA
authors.lastname: Bozhko
authors.affiliation: Fachbereich Physik and Landesforschungszentrum OPTIMAS, Technische Universität Kaiserslautern, 67663 Kaiserslautern, Germany.
authors.forename: Andrii V
authors.initials: AV
authors.lastname: Chumak
authors.affiliation: Fachbereich Physik and Landesforschungszentrum OPTIMAS, Technische Universität Kaiserslautern, 67663 Kaiserslautern, Germany.
authors.forename: Timo
authors.initials: T
authors.lastname: Neumann
authors.affiliation: Fachbereich Physik and Landesforschungszentrum OPTIMAS, Technische Universität Kaiserslautern, 67663 Kaiserslautern, Germany.
authors.forename: Björn
authors.initials: B
authors.lastname: Obry
authors.affiliation: Faculty of Radiophysics, Taras Shevchenko National University of Kyiv, 01601 Kyiv, Ukraine.
authors.forename: Gennadii A
authors.initials: GA
authors.lastname: Melkov
authors.affiliation: Department of Physics, Oakland University, Rochester, Michigan 48309, USA.
authors.forename: Andrei N
authors.initials: AN
authors.lastname: Slavin
authors.affiliation: Fachbereich Physik and Landesforschungszentrum OPTIMAS, Technische Universität Kaiserslautern, 67663 Kaiserslautern, Germany.
authors.forename: Burkard
authors.initials: B
authors.lastname: Hillebrands
mesh_terms: D000465:Algorithms; D055598:Chemical Phenomena; D005740:Gases / Q000737:chemistry*; D006358:Hot Temperature; D007700:Kinetics; D008962:Models, Theoretical; D044367:Phase Transition; D017785:Photons; D013816:Thermodynamics
chemical_list: D005740:Gases