Demokritov S O, Demidov V E, Dzyapko O, Melkov G A, Serga A A, Hillebrands B, Slavin A N
Institute for Applied Physics, University of Münster, 48149 Münster, Germany.
Nature. 2006 Sep 28;443(7110):430-3. doi: 10.1038/nature05117.
Bose-Einstein condensation is one of the most fascinating phenomena predicted by quantum mechanics. It involves the formation of a collective quantum state composed of identical particles with integer angular momentum (bosons), if the particle density exceeds a critical value. To achieve Bose-Einstein condensation, one can either decrease the temperature or increase the density of bosons. It has been predicted that a quasi-equilibrium system of bosons could undergo Bose-Einstein condensation even at relatively high temperatures, if the flow rate of energy pumped into the system exceeds a critical value. Here we report the observation of Bose-Einstein condensation in a gas of magnons at room temperature. Magnons are the quanta of magnetic excitations in a magnetically ordered ensemble of magnetic moments. In thermal equilibrium, they can be described by Bose-Einstein statistics with zero chemical potential and a temperature-dependent density. In the experiments presented here, we show that by using a technique of microwave pumping it is possible to excite additional magnons and to create a gas of quasi-equilibrium magnons with a non-zero chemical potential. With increasing pumping intensity, the chemical potential reaches the energy of the lowest magnon state, and a Bose condensate of magnons is formed.
玻色 - 爱因斯坦凝聚是量子力学所预言的最迷人的现象之一。如果粒子密度超过临界值，它涉及由具有整数角动量的相同粒子（玻色子）组成的集体量子态的形成。为了实现玻色 - 爱因斯坦凝聚，可以降低温度或增加玻色子的密度。据预测，如果泵入系统的能量流率超过临界值，玻色子的准平衡系统即使在相对较高的温度下也可能经历玻色 - 爱因斯坦凝聚。在此，我们报告了在室温下磁振子气体中玻色 - 爱因斯坦凝聚的观测结果。磁振子是磁有序磁矩集合体中磁激发的量子。在热平衡中，它们可以用具有零化学势和与温度相关密度的玻色 - 爱因斯坦统计来描述。在本文所展示的实验中，我们表明通过使用微波泵浦技术，可以激发额外的磁振子并创建具有非零化学势的准平衡磁振子气体。随着泵浦强度的增加，化学势达到最低磁振子态的能量，从而形成磁振子的玻色凝聚体。
