Burkard Hillebrands
A room-temperature magnon Bose-Einstein condensate (BEC) observed in magnetic insulators (single-crystal films of yttrium iron garnet, YIG) has a large potential in high-speed and low-power information processing and data transfer. At the same time, the miniaturization of magnon BEC-based magnonic devices constitutes an extraordinary challenge for their future applications.
We present a new and universal approach to enable Bose–Einstein condensation of magnons in confined systems [1]. The essential feature of this approach is the introduction of a disequilibrium of magnons with the phonon bath. After heating to an elevated temperature, a sudden decrease in the temperature of the phonons, which is approximately instant on the time scales of the magnon system, results in a large excess of incoherent magnons. The consequent spectral redistribution of these magnons triggers the Bose–Einstein condensation. We have observed this phenomenon by time-resolved Brillouin light scattering spectroscopy.
Moreover, we have studied by numerical simulations the formation of the magnon BEC in parametrically excited nanoscopic systems and proposed a new way to enhance condensate’s lifetime of by lateral confinement [2]. We revealed the role of dipolar interactions in the generation of a magnon BEC as a metastable state in YIG ultrathin film structures. We directly map out the nonlinear magnon scattering processes to show how fast quantized thermalization channels allow the BEC formation in confined structures.
Both our investigations greatly extends the freedom to study dynamics of magnon BEC in confined systems and to design integrated circuits for magnon BEC-based applications at room temperature.
[2] M. Mohseni et al., Bose-Einstein condensation of nonequilibrium magnons in confined systems, New J. Phys. 22, 083080 (2020).