Dresden 2009 – wissenschaftliches Programm
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MA: Fachverband Magnetismus
MA 2: Spin-Dynamics / Spin-Torque I
MA 2.4: Vortrag
Montag, 23. März 2009, 11:45–12:00, HSZ 04
Pumping free Bose-Einstein condensate of magnons — •Alexander A. Serga1, Vitaliy I. Vasyuchka1,2, Christian Sandweg1, Andrii V. Chumak1, Timo Neumann1, Gennadiy A. Melkov2, and Burkard Hillebrands1 — 1FB Physik and Forschungszentrum OPTIMAS, TU Kaiserslautern, Germany — 2National Taras Shevchenko University of Kiev, Ukraine
A free evolution of a Bose-Einstein condensate (BEC) of parametrically injected magnons after shutdown of a pumping microwave field was studied by means of time-resolved Brillouin light scattering spectroscopy in a tangentially magnetized yttrium-iron-garnet film at room temperature. The light scattered by the primary magnon group, which was parametrically excited near the frequency of ferromagnetic resonance, and by the BEC of magnons at the bottom of spin-wave spectrum was detected and analyzed in the time domain.
A pronounced and sharp (by a factor of 10 during 30 ns) intensity jump of the BEC of magnons above its equilibrium value has been detected just after the external pumping source was switched off. This jump was accompanied by the fast nonlinear decay of the primary magnon group with the relaxation time of 60 ns. The subsequent decay of the BEC of magnons is much slower and is characterized by the relaxation time of 800 ns. The discovered surge is interpreted as an increase in scattering efficiency of the parametrically injected magnons to the Bose-Einstein condensate in absence of pumping.
Financial support by the DFG (SFB/TRR 49) and by the Ukrainian Fund for Fundamental Research (No. 25.2/009) is acknowledged.