True Mechanism of Spontaneous Order from Turbulence in Two-Dimensional Superfluid Manifolds
True Mechanism of Spontaneous Order from Turbulence in Two-Dimensional Superfluid Manifolds
复制标题
二维超流体流形中湍流自发有序的真实机制
DOI：
10.1103/physrevlett.127.095301
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发表时间：
2021
影响因子：
8.6
通讯作者：
Guo, Wei
中科院分区：
文献类型：
--
作者：
Kanai, Toshiaki;Guo, Wei
在含有点状涡的二维湍流中，Lars Onsager预测，向流体中添加能量可以导致形成持久的类符号涡簇，即Onsager涡（OV）簇。在均匀盘状玻色-爱因斯坦凝聚体（BEC）中二维超流体湍流的演化过程中，发现在没有任何能量输入的情况下，可以形成一对符号相反的OV星团。这种惊人的自发秩序被解释为由于涡旋蒸发加热机制，即涡旋-反涡旋对的湮灭，消除了最低能量的涡旋，从而提高了每个涡旋的平均能量。然而，当我们在无边界的二维球形BEC中寻找奇异的OV态时，我们发现尽管涡旋对湮灭，OV星团也不会形成。我们的分析表明，与一般的看法相反，旋涡对湮灭发出强烈的声波，这抑制了所有旋涡的运动，从而抑制了OV团簇的形成。我们还提出了明确的证据，表明观察到的自发OV状态的真正机制是离开BEC边界的漩涡。揭示这一机制为全面理解远离平衡的二维超流体流形中的紧急旋涡顺序铺平了道路。
In a 2D turbulent fluid containing pointlike vortices, Lars Onsager predicted that adding energy to the fluid can lead to the formation of persistent clusters of like-signed vortices, i.e., Onsager vortex (OV) clusters. In the evolution of 2D superfluid turbulence in a uniform disk-shaped Bose-Einstein condensate (BEC), it was discovered that a pair of OV clusters with opposite signs can form without any energy input. This striking spontaneous order was explained as being due to a vortex evaporative-heating mechanism, i.e., annihilations of vortex-antivortex pairs which remove the lowest-energy vortices and thereby boost the mean energy per vortex. However, in our search for exotic OV states in a boundaryless 2D spherical BEC, we found that OV clusters never form despite the annihilations of vortex pairs. Our analysis reveals that contrary to the general belief, vortex-pair annihilation emits intense sound waves, which damp the motion of all vortices and hence suppress the formation of OV clusters. We also present unequivocal evidence showing that the true mechanism underlying the observed spontaneous OV state is the vortices exiting the BEC boundaries. Uncovering this mechanism paves the way for a comprehensive understanding of emergent vortex orders in 2D manifolds of superfluids driven far from equilibrium.