Dresden 2014 – scientific programme
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MA: Fachverband Magnetismus
MA 43: Magnetization Dynamics III
MA 43.7: Talk
Thursday, April 3, 2014, 16:45–17:00, HSZ 401
Condensation of mixed magnon-phonon states below the bottom of the magnon spectrum — •Dmytro A. Bozhko1, Alexander A. Serga1, Peter Clausen1, Vitaliy I. Vasyuchka1, Andrii V. Chumak1, Gennadii A. Melkov2, and Burkard Hillebrands1 — 1Fachbereich Physik and Landesforschungszentrum OPTIMAS, TU Kaiserslautern, Germany — 2Faculty of Radiophysics, Taras Shevchenko National University of Kyiv, Ukraine
The Brillouin light scattering technique is used to measure the distribution of a parametrically driven magnon gas in frequency and wavevector spaces. The experiment is performed utilizing an in-plane magnetized 6.7 µm thick single-crystal yttrium iron garnet film. A magnetizing field is tuned to excite the parametric magnons at the ferromagnetic resonance frequency of 6.8 GHz. In the case of a quasi-uniform pumping field, we are able to detect a strong magnon density peak around the bottom of the spin waves spectrum (4.8 GHz) at the hybridization area (8·104 rad/cm) between a backward volume magnetostatic wave and a transverse acoustic wave. This peak is understood as the condensation of magnon-phonon quasi-particles at a virtual energy minimum, whose frequency position is determined by magnon-phonon interaction. It is remarkable that no condensation is observed in the spatially localized pumping field: The magnon-phonon quasi-particles have a very high group velocity, and thus leave the thermalization area. Financial support by the DFG within the SFB/TR 49 is gratefully acknowledged.