Critical flow and dissipation in a quasi-one-dimensional superfluid.
Critical flow and dissipation in a quasi-one-dimensional superfluid.
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DOI：
10.1126/sciadv.1400222
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发表时间：
2015-05
期刊：
影响因子：
13.6
通讯作者：
Gervais G
中科院分区：
文献类型：
--
作者：
Duc PF;Savard M;Petrescu M;Rosenow B;Del Maestro A;Gervais G
超流通过纳米级管道的减速被测量和量化。在通用临界现象理论中最著名的例子之一，4He向超流体状态的相变与具有XY对称的经典自旋晶格中的铁磁性的开始属于相同的三维（3D） O(2)普适类。在过渡下，超流体密度ρs和超流体速度vs以温度的幂定律增加，该定律由一个通用临界指数描述，该指数被尺度不变性约束为相同。当维数向一维降低时，预期增强的热和量子涨落排除了长程有序，从而抑制了超流动性。在毛细管流动实验中，我们测量了液氦的流速，并推导了液氦在直径为20 ~ 3nm的30nm纳米孔中的超流速度。随着孔隙尺寸减小到一维极限，我们观察到以下现象：(i)超流体速度的压力依赖性受到抑制；（ii） vs的温度依赖性，令人惊讶的是，它可以在很宽的温度范围内用单指数幂律很好地拟合；（iii）当通道尺寸小于R≃20 nm时，临界速度随半径的减小而减小，这与微米尺寸的通道形成鲜明对比。我们将这些偏离体行为解释为信号交叉到准一维状态，其中关键拓扑缺陷的大小被通道半径切断。
The slowdown of a superflow through a nanoscale pipe is measured and quantified. In one of the most celebrated examples of the theory of universal critical phenomena, the phase transition to the superfluid state of 4He belongs to the same three-dimensional (3D) O(2) universality class as the onset of ferromagnetism in a lattice of classical spins with XY symmetry. Below the transition, the superfluid density ρs and superfluid velocity vs increase as a power law of temperature described by a universal critical exponent that is constrained to be identical by scale invariance. As the dimensionality is reduced toward 1D, it is expected that enhanced thermal and quantum fluctuations preclude long-range order, thereby inhibiting superfluidity. We have measured the flow rate of liquid helium and deduced its superfluid velocity in a capillary flow experiment occurring in single 30-nm-long nanopores with radii ranging down from 20 to 3 nm. As the pore size is reduced toward the 1D limit, we observe the following: (i) a suppression of the pressure dependence of the superfluid velocity; (ii) a temperature dependence of vs that surprisingly can be well-fitted by a power law with a single exponent over a broad range of temperatures; and (iii) decreasing critical velocities as a function of decreasing radius for channel sizes below R ≃ 20 nm, in stark contrast with what is observed in micrometer-sized channels. We interpret these deviations from bulk behavior as signaling the crossover to a quasi-1D state, whereby the size of a critical topological defect is cut off by the channel radius.