Neutron Scattering Experiments and Path Integral Monte Carlo Studies of Disordered Quantum Systems

9972011Glyde这是一个凝聚态物理项目，使用非弹性中子散射测量和路径积分蒙特卡罗模拟技术来研究无序玻色量子液体的基本激发。将液体4He和3He/4He混合物限制在高孔气凝胶中会引起无序。我们的目标是确定无序引起的新特征，如新的低能激发，色散曲线上的间隙，有限的激发寿命，以及这些特征与超流密度、玻色凝聚和凝聚体可能的局域化之间的关系。在同一无序物质中，动量分布和凝聚态分数将用相同的技术独立测量和计算。无序受限液体4He的热力学和标度性质已经研究了40年，但还没有一个并行的程序来观察激发。该项目使用了劳厄·朗之万研究所(法国格勒诺布尔)和ISIS设施在卢瑟福·阿普尔顿实验室(牛津，英国)的先进的中子衍射方法。这项工作为研究生和博士后助理提供了极好的培训。%该项目使用中子衍射方法来研究液氦在气凝胶等高度多孔的介质中受限时的性质。气凝胶的存在通过限制氦在丝状二氧化硅气凝胶网络中的“运动”来改变氦的性质。声音在氦中的传播会受到影响，液体的运动以及氦的密度都会受到二氧化硅网络的影响。在受限几何结构中发现的氦的性质将与大体积液体的类似信息进行比较。这些信息对量子力学和理解液氦的超流体性质具有根本意义。该项目使用了劳厄·朗之万研究所(法国格勒诺布尔)和ISIS设施在卢瑟福·阿普尔顿实验室(牛津，英国)的先进的中子衍射方法。这项工作为研究生和博士后助理提供了极好的培训。

9972011GlydeThis is a condensed matter physics project that employs inelastic neutron scattering measurements and Path Integral Monte Carlo simulation techniques to study the elementary excitations of Bose quantum liquids in disorder. Disorder is induced by confining liquid 4He and 3He/4He mixtures in highly porous aerogel. The object is to determine the new features induced by disorder such as new low energy excitations, a gap in the dispersion curve, finite excitation lifetimes and how these features relate to the superfluid density, to Bose condensation and possible localization of the condensate. The momentum distribution and the condensate fraction in the same disordered materials will be measured and calculated independently by the same techniques. Thermodynamic and scaling properties of disordered and confined liquid 4He have been studied for 40 years, but there has been no parallel program to observe excitations. This project uses sophisticated neutron diffraction methods at the Institute Laue Langevin (Grenoble, France) and the ISIS facility at the Rutherford Appleton Laboratory (Oxford, UK). The work provides excellent training for graduate students and post-doctoral associates.%%%This project uses neutron diffraction methods to investigate the properties of liquid helium when the helium is confined in highly porous media like aerogel. The presence of the aerogel modifies the properties of the helium by restricting the 'motion' of the helium in the filamentous silica aerogel network. The propagation of sound in helium is affected, liquid motions, as well as the density of helium is affect by the silica network. The properties of helium found in the confined geometry will be compared with similar information for the bulk liquid. The information is of fundamental interest for quantum mechanics and for understanding the superfluid nature of liquid helium. This project uses sophisticated neutron diffraction methods at the Institute Laue Langevin (Grenoble, France) and the ISIS facility at the Rutherford Appleton Laboratory (Oxford, UK). The work provides excellent training for graduate students and post-doctoral associates.