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Phonon-roton modes of liquid ~4He beyond the roton in the porous medium MCM-41

机译：多孔介质中MCM-41以外的液态〜4He的声子-质子模式

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摘要

We present neutron scattering measurements of the phonon-roton (P-R) mode of superfluid ~4He confined in 47 AMCM-41 at T = 0.5 K at wave vectors, Q, beyond the roton wave vector (Q_R = 1.92 A~(-1)). Measurements beyond the roton require access to high wave vectors (up to Q = 4 A~(-1)) with excellent energy resolution and high statistical precision. Only one previous measurement in porous media (in aerogel) with low statistical precision has been reported. At T = 0.5 K, we find that the P-R mode in MCM-41 extends out to wave vector Q approx= 3.6 A~(-1), with the same energy and zero width (within precision) as observed in bulk superfluid ~4He. Layer modes in the roton region are also observed. Specifically, the P-R mode energy, ω_Q, increases with Q for Q ＞ Q_R and reaches a plateau at a maximum energy ω_Q = 2A where △ is the roton energy, △ = 0.74 ± 0.01 meV in MCM-41. This upper limit means the P-R mode decays to two rotons if its energy exceeds 2 △. It also means that the P-R mode does not decay to two-layers modes. If the P-R could decay to two-layer modes, ω_Q would plateau at a lower energy, ω_Q = 2△_L, where △_L = 0.60 meV is the energy of the roton-like minimum of the layer mode. Rather the P-R mode and the layer modes observed in porous media appear to be quite different modes with little interaction between them.
机译：我们提出了超流体〜4He的声子-鲁顿（PR）模式的中子散射测量结果，其波矢量Q限制在47 AMCM-41的T = 0.5 K处，超出了质子波矢量（Q_R = 1.92 A〜（-1） ）。超出测速仪的测量需要获得具有出色能量分辨率和高统计精度的高波矢（高达Q = 4 A〜（-1））。据报道，以前在多孔介质（气凝胶中）中的一种测量方法的统计精度较低。在T = 0.5 K时，我们发现MCM-41中的PR模式扩展到波矢量Q大约= 3.6 A〜（-1），具有与在体超流体〜4He中观察到的相同的能量和零宽度（精度范围内） 。还可以观察到roton区域中的层模式。具体而言，对于Q＞ Q_R，P-R模式能量ω_Q随着Q的增加而增加，并在最大能量ω_Q= 2A时达到平稳，其中△是ro子能量，在MCM-41中为△= 0.74±0.01 meV。该上限意味着，如果P-R模式的能量超过2△，它会衰减到两个roton。这也意味着P-R模式不会衰减到两层模式。如果P-R可以衰减到两层模式，则ω_Q将在较低的能量处达到平稳，ω_Q= 2△_L，其中△_L = 0.60 meV是层模式的类似于ro子的最小值的能量。而是在多孔介质中观察到的P-R模式和层模式似乎是完全不同的模式，它们之间几乎没有相互作用。

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  • 来源
    《Physical review》 |2013年第2期|024510.1-024510.8|共8页
  • 作者

    R. T. Azuah; S. O. Diallo; M. A. Adams; O. Kirichek; H. R. Glyde;

  • 作者单位

    NIST Center for Neutron Research, Gaithersburg, Maryland 20899-8562, USA,Department of Materials Science and Engineering, University of Maryland, College Park, Maryland 20742-2115, USA;

    Department of Physics and Astronomy, University of Delaware, Newark, Delaware 19716-2593, USA,Quantum Condensed Matter Division, Oak Ridge National Labora-tory, Oak Ridge, TN 37831, USA;

    ISIS Spoliation Neutron Source, Rutherford Appleton Laboratory, Chilton, Didcot, OX11 0QX, United Kingdom;

    ISIS Spoliation Neutron Source, Rutherford Appleton Laboratory, Chilton, Didcot, OX11 0QX, United Kingdom;

    Department of Physics and Astronomy, University of Delaware, Newark, Delaware 19716-2593, USA;

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