低频下无压力驱动的超固体流动
Absence of Pressure-Driven Supersolid Flow at Low Frequency
摘要：
超固体研究中一个重要的未解决的问题是在Kim和Chan的扭振子实验中观察到的非经典转动惯量（NCRI）现象在多大程度上是具有超流体性质的玻色凝聚超固态的证据。在一个开放的环形几何形状，Kim和Chan发现，固体的一小部分转动惯量是从振荡器的运动解耦;然而，当环被一个分区阻塞，解耦的超固体部分被锁定到振荡器被加速由移动分区产生的AC压力梯度。这些观测结果与超流流体动力学理论是一致的。我们应用低频交流压力梯度，以寻找超流体样的响应在超固体样品。我们的结果是一致的零超固体流动的低频压力梯度。我们的数据集的统计分析的约束，在68%的置信水平，9.6 $\times 10^{-4}$ nm/s的质量传输速度进行的一个可能的超固体流。根据超固体的简单模型，在25 mK下，在相同的置信水平下，超固体分数的上限设定为3.3 $\times 10^{-6}$。这些发现迫使我们得出这样的结论，即在扭振子实验中观察到的NCRI并不是频率无关的超流状态的证据。超固体行为是一种频率依赖性现象，在扭转振荡器实验的频率范围内非常明显，但在接近零的频率下不可检测。
英文摘要：
An important unresolved question in supersolid research is the degree to which the non-classical rotational inertia (NCRI) phenomenon observed in the torsional oscillator experiments of Kim and Chan, is evidence for a Bose-condensed supersolid state with superfluid-like properties. In an open annular geometry, Kim and Chan found that a fraction of the solid moment of inertia is decoupled from the motion of the oscillator; however, when the annulus is blocked by a partition, the decoupled supersolid fraction is locked to the oscillator being accelerated by an AC pressure gradient generated by the moving partition. These observations are in accord with superfluid hydrodynamics. We apply a low frequency AC pressure gradient in order to search for a superfluid-like response in a supersolid sample. Our results are consistent with zero supersolid flow in response to the imposed low frequency pressure gradient. A statistical analysis of our data sets a bound, at the 68% confidence level, of 9.6$\times 10^{-4}$ nm/s for the mass transport velocity carried by a possible supersolid flow. In terms of a simple model for the supersolid, an upper bound of 3.3$\times 10^{-6}$ is set for the supersolid fraction at 25 mK, at this same confidence level. These findings force the conclusion that the NCRI observed in the torsional oscillator experiments is not evidence for a frequency independent superfluid-like state. Supersolid behavior is a frequency-dependent phenomenon, clearly evident in the frequency range of the torsional oscillator experiments, but undetectably small at frequencies approaching zero.
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