Advances in observation of linear and nonlinear magnon spectra using Brillouin light scattering spectroscopy
December 12, 2023 @ 11:00 am - 12:00 pm CST
Zoom link: https://argonne.zoomgov.com/j/1609918220
Time: December 12, 11am-12pm Central Time
Speaker: Dmytro A. Bozhko
Center for Magnetism and Magnetic Nanostructures, Department of Physics and Energy Science
University of Colorado Colorado Springs, Colorado Springs, CO 80918, USA
Wave interactions are responsible for the various aspects of the behavior of different systems in nature, including processes in the Earth’s ocean and atmosphere, dynamics of stars, and even the evolution of the Universe. Spin waves (and their quanta–magnons) in magnetically ordered materials are highly nonlinear compared to, for example, phonons or photons in solids. One of the most suitable systems for studying magnons is single-crystalline ferrimagnetic yttrium iron garnet (YIG, Y3Fe5O12) and in particular, films made out of it. The strong nonlinearity, combined with the high quality factor of magnons in YIG, facilitates the observation of various types of nonlinear interaction processes [1–3]. For example, the phenomenon of Bose-Einstein condensation of magnons at the bottom of their frequency spectrum, observed in YIG films [4,5], has provided significant assistance in these studies. In our experiments, this condensation was achieved by two experimental techniques – the parametric pumping of magnons with microwave radiation [5] and the rapid cooling [6] methods.
In the currently presented study, I will show the construction of a 3D-printed setup for 2D wavevector-resolved Brillouin light scattering spectroscopy. Using this setup, it became possible to directly measure for the first time the full spin wave dispersion of thin YIG film in 2D. Also, we were able to register the results of several novel nonlinear processes that involve not only “real” quasiparticles (the eigenmodes of the medium) but produce as a final product virtual quasiparticles (out-of-spectrum waves) caused by various types of nonlinear interactions. The most nontrivial and intriguing process involves a pair of parametrically excited magnons and a partially coherent Bose-Einstein condensate (BEC). This process is enhanced by full phase correlations in parametric magnon pairs with opposite wavevectors [7].
[1] O. V. Prokopenko et al., Recent Trends in Microwave Magnetism and Superconductivity, Ukr. J. Phys. 64, 888 (2019).
[2] A. V. Chumak et al., Roadmap on Spin-Wave Computing, IEEE Trans. Magn. 58, 0800172 (2022).
[3] A. J. E. Kreil et al., Tunable Space-Time Crystal in Room-Temperature Magnetodielectrics, Phys. Rev. B 100, 020406 (2019).
[4] S. O. Demokritov et al., Bose–Einstein Condensation of Quasi-Equilibrium Magnons at Room Temperature under Pumping, Nature 443, 430 (2006).
[5] A. A. Serga et al., Bose–Einstein Condensation in an Ultra-Hot Gas of Pumped Magnons, Nat. Commun. 5, 3452 (2014).
[6] M. Schneider et al., Bose–Einstein Condensation of Quasiparticles by Rapid Cooling, Nat. Nanotechnol. 15, 457 (2020).
[7] V. S. L’vov et al., Correlation-Enhanced Interaction of a Bose-Einstein Condensate with Parametric Magnon Pairs and Virtual Magnons, Phys. Rev. Lett. 131, 156705 (2023).
Biography
Dr. Bozhko received his B.Sc. and M.Sc. in physics from the Taras Shevchenko National University of Kyiv in 2013, and his doctorate in physics from the Technische Universität Kaiserslautern in 2017. After postdoctoral work first at TU Kaiserslautern and after that at the University of Glasgow, he joined the faculty of the Department of Physics and Energy Science at the University of Colorado Colorado Springs in 2019, where he now holds the rank of Assistant Professor. Dr. Bozhko is the author of over 38 refereed publications. His experimental studies in the areas of linear, nonlinear, and quantum magnonics are funded by the National Science Foundation and the Department of Energy.
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