Institute for Applied Physics and Center for Nonlinear Science, University of Muenster, Corrensstr. 2-4, 48149 Muenster, Germany.
Sci Rep. 2012;2:482. doi: 10.1038/srep00482. Epub 2012 Jun 29.
A gas of magnons in magnetic films differs from all other known systems demonstrating Bose-Einstein condensation (BEC), since it possesses two energetically degenerate lowest-energy quantum states with non-zero wave vectors ±k(BEC). Therefore, BEC in this system results in a spontaneously formed two-component Bose-Einstein condensate described by a linear combination of two spatially non-uniform wave-functions ∝exp(±ik(BEC)z), while condensates found in other physical systems are characterized by spatially uniform wave-functions. Here we report a study of BEC of magnons with sub-micrometer spatial resolution. We experimentally confirm the existence of the two wave-functions and show that their interference results in a non-uniform ground state of the condensate with the density oscillating in space. Additionally, we observe stable topological defects in the condensate. By comparing the experimental results with predictions of a theoretical model based on the Ginzburg-Landau equation, we identify these defects as quantized vortices.
在磁性薄膜中的磁振子气体与所有其他展示玻色-爱因斯坦凝聚（BEC）的已知系统不同，因为它具有两个能量简并的最低能量量子态，其波矢不为零 ±k（BEC）。因此，在这个系统中的 BEC 导致了由两个空间不均匀波函数的线性组合∝exp(±ik（BEC）z）描述的自发形成的两分量玻色-爱因斯坦凝聚，而在其他物理系统中发现的凝聚态则具有空间均匀的波函数。在这里，我们报告了对具有亚微米空间分辨率的磁振子 BEC 的研究。我们通过实验证实了这两个波函数的存在，并表明它们的干涉导致了凝聚态的非均匀基态，其密度在空间中振荡。此外，我们观察到凝聚体中的稳定拓扑缺陷。通过将实验结果与基于吉布斯-朗道方程的理论模型的预测进行比较，我们将这些缺陷识别为量子涡旋。
