paper

Bose-Einstein Condensation of Quasi-Particles by Rapid Cooling

arXiv:1612.07305 · doi:10.1038/s41565-020-0671-z

Abstract

The fundamental phenomenon of Bose-Einstein Condensation (BEC) has been observed in different systems of real and quasi-particles. The condensation of real particles is achieved through a major reduction in temperature while for quasi-particles a mechanism of external injection of bosons by irradiation is required. Here, we present a novel and universal approach to enable BEC of quasi-particles and to corroborate it experimentally by using magnons as the Bose-particle model system. The critical point to 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.

arXiv commentIn contrast to the previous version additional information has been added. The chemical potential was derived from BLS measurements, the influence of the spin Seebeck effect is discussed more extensively in the Supplement with respect to the theoretical model and the rapid cooling has been realized in Au/Al/YIG structures where no substantial contribution of the spin Seebeck effect is expected

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