Berlin 2018 – wissenschaftliches Programm
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MA: Fachverband Magnetismus
MA 27: Spin currents and spin torques
MA 27.7: Vortrag
Mittwoch, 14. März 2018, 11:00–11:15, EB 407
From kinetic instability to Bose-Einstein condensation and magnon supercurrent — •Halyna Yu. Musiienko-Shmarova1, Alexander J.E. Kreil1, Dmytro A. Bozhko1, Victor S. L’vov2, Anna Pomyalov2, Burkard Hillebrands1, and Alexander A. Serga1 — 1Fachbereich Physik and Landesforschungszentrum OPTIMAS, TU Kaiserslautern, Germany — 2Department of Chemical Physics, Weizmann Institute of Science, Rehovot 76100, Israel
By means of electromagnetic parametric pumping an ensemble of magnons, quanta of spin waves, can be prepared as an overpopulated Bose gas of weakly interacting quasiparticles. The evolution of this gas via magnon-magnon scattering processes can lead to the formation of a Bose-Einstein condensate (BEC) at the bottom of spin-wave spectrum. We studied this phenomena experimentally (by Brillouin light scattering spectroscopy) and theoretically in an yttrium-iron-garnet film in a wide region of the external magnetic field. This allows us to compare features of the condensation process in the cases when one of two physical mechanisms of the magnon transfer from a pumped high-frequency area to the BEC state prevails: a step-by-step Kolmogorov-Zakharov cascade of weak wave turbulence process or a kinetic-instability channel, which directly transfers magnons from the pumping area to the BEC point. As a result, we demonstrate the formation of a coherent condensed magnon state even in the presence of the kinetic instability processes leading to a strongly unbalanced non-equilibrium population of the low-energy part of the magnon spectrum. Financial support from the ERC Advanced Grant "SuperMagnonics" is acknowledged.