突破超流体速度极限
Breaking the superfluid speed limit
摘要：
在许多系统中，相干凝聚体作为涌现现象出现，共享将最低激发与凝聚体基态分离的能隙的特征。这意味着散射物体以足够高的速度移动通过系统，使散射帧中的激发光谱变得无间隙，可以在没有能量成本的情况下产生激发，引发凝聚体的分解。这个极限就是著名的朗道速度。虽然，中性费米超流3 He-B在T=0的限制，围绕振荡体的流动显示出一个非常明确的临界速度耗散的开始，在这里，我们表明，对于均匀的线性运动有没有不连续的耗散朗道临界速度通过和超过。由于朗道速度是我们理解超流性的支柱，这是一个相当大的惊喜，对理解所有相干凝聚系统中运动物体的耗散效应具有意义。
英文摘要：
Coherent condensates appear as emergent phenomena in many systems, sharing the characteristic feature of an energy gap separating the lowest excitations from the condensate ground state. This implies that a scattering object, moving through the system with high enough velocity for the excitation spectrum in the scatter frame to become gapless, can create excitations at no energy cost, initiating the breakdown of the condensate. This limit is the well-known Landau velocity. While, for the neutral Fermionic superfluid 3He-B in the T=0 limit, flow around an oscillating body displays a very clear critical velocity for the onset of dissipation, here we show that for uniform linear motion there is no discontinuity whatsoever in the dissipation as the Landau critical velocity is passed and exceeded. Since the Landau velocity is such a pillar of our understanding of superfluidity, this is a considerable surprise, with implications for the understanding of the dissipative effects of moving objects in all coherent condensate systems.
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