Bose-Einstein Condensation of Quasi-Particles by Rapid Cooling
  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. 
M. Schneider, T. Br\"acher, D. Breitbach, V. Lauer, P. Pirro, D. A.   Bozhko, A. A. Serga, H. Yu. Musiienko-Shmarova, B. Hei...
cond-mat.mes-hall cond-mat.other