Neutron Scattering Studies of Quantum Systems

这是一个凝聚态物理项目，研究液氦、4He以及3He和4He混合物的低温性质。这项研究将使用中子散射方法来研究无序多孔玻璃中的限制对氦性质的影响。如果感兴趣的是(1)无序和限制对超流相的作用，其中先前的研究已经表明限制引起的宏观变化反映在微观动力学中；(2)限制对3He-4He混合物中发生的相分离的影响，其中宏观研究表明三临界点成为规则的临界点；以及(3)当限制在多孔介质中时的固相结构，其中初步研究表明无序在相图上比在块体中更大的区域内稳定bcc相。中子散射测量，如弹性和非弹性散射，为这些系统的微观动力学提供了一个强大的探测器。使用这些技术可以很容易地探测到原子结构、集体激发和单粒子动量分布等性质。这项研究涉及与劳埃朗之万研究所(法国格勒诺布尔)的工作人员、阿普尔顿卢瑟福实验室(英国牛津大学)的ISIS散裂源以及美国的中子源的合作。这项研究使用最先进的仪器为基础研究领域的研究生提供了极好的培训。%量子流体氦-3和氦-4为研究服从玻色和费米统计的强相互作用粒子集合提供了独特的“实验室”。中子散射测量，如弹性和非弹性散射，为这些系统的微观动力学提供了一个强大的探测器。使用这些技术可以很容易地探测到原子结构、集体激发和单粒子动量分布等性质。这个项目试图了解无序的大块氦或氦混合物如何影响流体的性质。无序是通过添加杂质，通过将流体浸入高度多孔的气凝胶或Vycor玻璃中，或者通过热波动来引入的。中子散射实验独特而灵敏地表明，氦的一些基本性质因这种无序而改变。这项研究涉及与劳埃朗之万研究所(法国格勒诺布尔)的工作人员、阿普尔顿卢瑟福实验室(英国牛津大学)的ISIS散裂源以及美国的中子源的合作。这项研究为研究生在基础研究领域使用最先进的仪器提供了极好的培训。

9970126SokolThis is a condensed matter physics project dealing with the low temperature properties of liquid helium, 4He, and mixtures of 3He and 4He. The investigation will use neutron scattering methods to study the effect of confinement in disordered porous glasses on the properties of helium. If interest are (1) the role of disorder and confinement on the superfluid phase where previous studies have already shown that the macroscopic changes induced by confinement are mirrored in the microscopic dynamics; (2) the effects of confinement on the phase separation that occurs in 3He-4He mixtures where macroscopic studies have shown that the tricritical point becomes a regular critical point; and (3) the structure of the solid phase when confined in porous media where preliminary studies have shown that disorder stabilizes the bcc phase over a much larger region of the phase diagram than in the bulk. Neutron scattering measurements, such as elastic and inelastic scattering, provide a powerful probe of the microscopic dynamics of these systems. Properties such as the atomic structure, collective excitations, and single particle momentum distribution can be readily probed using these techniques. The research involves collaborations with workers at the Institut Laue Langevin (Grenoble, France), and the ISIS spallation source at the Appleton Rutherford Laboratory (Oxford, UK), as well as neutron sources in the US. The research provides excellent training for graduate students in a fundamental research area using state-of-the-art instrumentation.%%%The quantum fluids helium-3 and helium-4 provide a unique 'laboratory' for the study of strongly interacting assemblies of particles obeying Bose and Fermi statistics. Neutron scattering measurements, such as elastic and inelastic scattering, provide a powerful probe of the microscopic dynamics of these systems. Properties such as the atomic structure, collective excitations, and single particle momentum distribution can be readily probed using these techniques. This project seeks to understand how disordering bulk helium or helium mixtures influences the fluids' properties. Disorder is introduced either through the addition of impurities, by immersing the fluid in highly porous aerogel or Vycor glass, or through thermal fluctuations. Neutron scattering experiments uniquely and sensitively show that a number of the fundamental properties of helium are changed by the disorder. The research involves collaborations with workers at the Institut Laue Langevin (Grenoble, France), and the ISIS spallation source at the Appleton Rutherford Laboratory (Oxford, UK), as well as neutron sources in the US. The research provides excellent training for graduate students in a fundamental research area using state-of-the-art instrumentation.