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Observation of first and second sound in a BKT superfluid

机译：在BKT Superfluid中观察第一和第二声音

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摘要

First and second sound are experimentally observed in a two-dimensional superfluid, and the temperature-dependent sound speeds reveal the predicted jump in the superfluid density at the infinite-order Berezinskii-Kosterlitz-Thouless transition.Superfluidity in its various forms has been of interest since the observation of frictionless flow in liquid helium II1,2. In three spatial dimensions it is conceptually associated with the emergence of long-range order at a critical temperature. One of the hallmarks of superfluidity, as predicted by the two-fluid model(3,4) and observed in both liquid helium(5) and in ultracold atomic gases(6,7), is the existence of two kinds of sound excitation-the first and second sound. In two-dimensional systems, thermal fluctuations preclude long-range order(8,9); however, superfluidity nevertheless emerges at a non-zero critical temperature through the infinite-order Berezinskii-Kosterlitz-Thouless (BKT) transition(10,11), which is associated with a universal jump(12) in the superfluid density without any discontinuities in the thermodynamic properties of the fluid. BKT superfluids are also predicted to support two sounds, but so far this has not been observed experimentally. Here we observe first and second sound in a homogeneous two-dimensional atomic Bose gas, and use the two temperature-dependent sound speeds to determine the superfluid density of the gas(13-16). Our results agree with the predictions of BKT theory, including the prediction of a universal jump in the superfluid density at the critical temperature.
机译：第一和第二声音在二维超流被实验观察到，并且取决于温度的声速揭示在无限阶Berezinskii-科斯特利茨-Thouless transition.Superfluidity各种形式的超流体密度所预测的跳跃一直感兴趣因为摩擦流在液态氦II1,2观察。在三个空间维度它在概念上以长程有序的在临界温度的出现相关联。一种超流的标志，如由双流体模型（3,4）预测和在液体氦（5）和在超冷原子气体（6,7）观察到，有两种声音excitation-的存在所述第一和第二声音。在两维系统，热波动排除长程有序（8,9）;然而，尽管如此，超流处出现通过无限阶Berezinskii-科斯特利茨-Thouless（BKT）转换（10,11），其与在超流密度在通用跳跃（12）而没有任何不连续性相关联的非零临界温度的流体的热力学性质。 BKT超流体也预计支持两种声音，但到目前为止，这还没有被实验观察到。在这里，我们观察到均匀的二维原子玻色气体在第一和第二声音，并使用两个温度相关声速确定气体（13-16）的超流体密度。我们的研究结果同意BKT理论的预言，包括在临界温度在超流体密度普遍跳跃的预测。

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  • 来源
    《Nature》 |2021年第7862期|191-194|共4页
  • 作者

    Christodoulou Panagiotis; Galka Maciej; Dogra Nishant; Lopes Raphael; Schmitt Julian; Hadzibabic Zoran;

  • 作者单位

    Univ Cambridge Cavendish Lab Cambridge England;

    Univ Cambridge Cavendish Lab Cambridge England;

    Univ Cambridge Cavendish Lab Cambridge England;

    ENS PSL Res Univ Coll France Sorbonne Univ Lab Kastler Brossel CNRS Paris France;

    Univ Cambridge Cavendish Lab Cambridge England|Univ Bonn Inst Angew Phys Bonn Germany;

    Univ Cambridge Cavendish Lab Cambridge England;

  • 收录信息 美国《科学引文索引》(SCI);美国《工程索引》(EI);美国《生物学医学文摘》(MEDLINE);美国《化学文摘》(CA);
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