Critical and surface phenomena of quantum fluids

量子流体的临界现象和表面现象

基本信息

批准号：
EP/F021429/1
负责人：
Peter Vaughan Elsmere McClintock
金额：
$ 15.38万
依托单位：
Lancaster University
依托单位国家：
英国
项目类别：
Research Grant
财政年份：
2008
资助国家：
英国
起止时间：
2008 至无数据
项目状态：
已结题

来源：
https://gtr.ukri.org/projects?ref=EP%2FF021429%2F1
关键词：
Critical surface phenomena quantum fluids

项目摘要

Neutron scattering provides a powerful tool for investigation of excitations in condensed matter. As a technique, it offers special advantages in the case of quantum fluids (liquid He4, liquid He3, and liquid isotopic mixtures). It can be applied both to excitations in the bulk and to those on the free surface of the fluid.The current research plan consists of two main parts:1. investigation of critical phenomena in He3, He4, and He3-He4 mixtures; and2. exploration of the possibility of using neutron reflection for studying quantum excitations on the surfaces of quantum fluids in the ultra-low temperature limit. The use of neutrons to study phenomena such as critical opalescence has special advatantages, compared to the traditional optical technique. In particular, it does not require the already-complicated cryogenic equipment to have optical windows. For example proposed method allows studies of the critical behaviour of fluid 3He and 3He-4He mixtures. Measurements of neutron opalescence in the vicinity of the critical point promise a rigorous test of the exact predictions of Renormalization Group theory, including several different classes of critical phenomena. We also wish to establish how the critical phenomena change if we place the fluid inside a nanoporous material: how the size of the critical fluctuations will be affected by the dimension of the host nano-matrix. Neutrons provide unique probes for this kind of research, especially at low temperatures.We now propose the use of neutron reflection to study the liquid helium surface, enabling us to test the long-standing theory of Fomin that, in the high-frequency limit, the Fermi liquid should support, not only ordinary capillary waves, but Rayleigh-type waves as well. It seems likely that unpredicted, unforeseen, physical effects will be observed as well. Slow neutrons exhibit a range of phenomena closely analogous to those observed in classical optics, including reflection, refraction and interference. Total reflection of slow neutrons was first reported by Fermi and co-workers and has since been extensively applied to a diversity of problems. For example the propagation and attenuation characteristics of surface acoustic waves have been experimentally investigated by neutron diffraction . To our knowledge, however, this method has not yet been applied to studies of the surfaces of quantum fluids, probably on account of the difficulty of combining a neutron reflectometer (e.g. CRISP at ISIS RAL) with the necessary ultra-low temperature sample environment. The investigation of the formation of Andreev's quantum states of 3He atoms on free surface of liquid 4He is another challenge of this research. We will also use neutron scattering to investigate wave turbulence on the surfaces of quantum fluids. The analogous optical experiment has already been carried out for a liquid hydrogen free surface, but no results have yet been reported for either He4 or He3.

中子散射为调查冷凝物质的激发提供了强大的工具。作为一种技术，它在量子液（液体HE4，液体HE3和液体同位素混合物）的情况下具有特殊的优势。它既可以应用于整体的激发和流体自由表面的激发。当前的研究计划由两个主要部分组成：1。调查HE3，HE4和HE3-HE4混合物中的关键现象；和2。探索使用中子反射以在超低温度极限下研究量子流体表面上的量子激发的可能性。与传统的光学技术相比，使用中子来研究诸如关键蛋白质的现象具有特殊的趋势。特别是，它不需要已经复杂的低温设备具有光窗。例如，提出的方法允许研究流体3HE和3HE-4HE混合物的临界行为。临界点附近中子乳白色的测量有望对重新归一化群体理论的确切预测进行严格测试，包括几种不同类别的关键现象。我们还希望确定如果将流体放入纳米多孔材料中：临界现象的变化是如何变化的：临界波动的大小将如何受宿主纳米矩阵的尺寸影响。中子为这类研究提供了独特的探针，尤其是在低温下。我们现在建议使用中子反射来研究液氦表面，从而使我们能够测试长期存在的福明素理论，即在高频限制下，费米液应该支持普通的毛细管，而是雷尔·毛细管，还应支持雷尔级波浪。似乎也可能会观察到不可预测的，无法预料的身体影响。缓慢的中子表现出一系列现象与经典光学器件中观察到的现象相似，包括反射，折射和干扰。费米和同事首先报道了慢速中子的总反射，此后已广泛应用于各种问题。例如，通过中子衍射对表面声波的传播和衰减特征进行了实验研究。然而，据我们所知，该方法尚未应用于量子流体表面的研究，这可能是由于将中子反射计（例如ISIS RAL的酥脆）与必要的超低温度样品环境相结合的难度。对4HE液体自由表面的3he原子的Andreev量子状态的形成的研究是这项研究的另一个挑战。我们还将使用中子散射来研究量子流体表面上的波湍流。已经针对无液体的表面进行了类似的光学实验，但尚未报告HE4或HE3的结果。