Bose–Einstein condensation in an ultra-hot gas of pumped magnons
Bose–Einstein condensation in an ultra-hot gas of pumped magnons
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DOI：
10.1038/ncomms4452
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发表时间：
2014-03
影响因子：
16.6
通讯作者：
A. Serga;V. Tiberkevich;C. W. Sandweg;V. Vasyuchka;D. Bozhko;A. Chumak;T. Neumann;B. Obry;G. Melkov;A. Slavin;B. Hillebrands
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作者：
A. Serga;V. Tiberkevich;C. W. Sandweg;V. Vasyuchka;D. Bozhko;A. Chumak;T. Neumann;B. Obry;G. Melkov;A. Slavin;B. Hillebrands
准粒子如激子、极化激元、磁振子和光子的玻色-爱因斯坦凝聚是一种有趣的量子力学现象。与真实的粒子（如原子）的玻色-爱因斯坦凝聚不同，这些过程不需要低温，因为凝聚体形成所需的低能量准粒子的高密度可以通过外部泵浦产生。在这里，我们证明，这样的泵可以创建非常高的有效温度在一个狭窄的光谱区域的最低能量状态的磁振子气体，导致惊人的意外过渡动力学的玻色-爱因斯坦磁振子凝聚体：密度的凝聚体后立即增加外部磁振子流被关闭，最初降低，如果它再次打开。这种行为可以在非线性的“蒸发过冷”机制中找到解释，该机制将通过与所有其他热磁振子泵浦而过热的低能磁振子耦合，去除多余的热量，并允许玻色-爱因斯坦凝聚形成。
Bose–Einstein condensation of quasi-particles such as excitons, polaritons, magnons and photons is a fascinating quantum mechanical phenomenon. Unlike the Bose–Einstein condensation of real particles (like atoms), these processes do not require low temperatures, since the high densities of low-energy quasi-particles needed for the condensate to form can be produced via external pumping. Here we demonstrate that such a pumping can create remarkably high effective temperatures in a narrow spectral region of the lowest energy states in a magnon gas, resulting in strikingly unexpected transitional dynamics of Bose–Einstein magnon condensate: the density of the condensate increases immediately after the external magnon flow is switched off and initially decreases if it is switched on again. This behaviour finds explanation in a nonlinear ‘evaporative supercooling’ mechanism that couples the low-energy magnons overheated by pumping with all the other thermal magnons, removing the excess heat, and allowing Bose–Einstein condensate formation.