Helium Films: Localization and Transitions

*非技术摘要*这个项目的重点是使用液氦研究氦的基本方面，以及使用氦的不寻常性质来探索凝聚态物理更广泛领域的重要问题。非常薄的氦薄膜在低于零下456华氏度的温度下成为一种无摩擦的超流体，并支持波，其作用很像微小的潮汐波。局部化是一种具有广泛重要性的现象，它是一种波被无序环境限制的现象。这种重要性从基本的(原子在光学陷阱中的行为)到应用(光在信号处理和光子学领域的技术领域的行为)。该项目寻求实验证据，证明在无序环境中，当支持波的流体直接流动时，波在氦薄膜上的基本局部化行为发生了变化。在另一个方向上，早期的工作表明，当两种氦原子(稀有的氦-3和更常见的氦-4)的薄膜在低温下位于光滑的固体氢表面上时，除了通常的超流体去耦合外，还有一种意想不到的原子与表面的去耦合。这表明了一种令人兴奋的可能性，即这类薄膜中可能发生了一种不同于通常的超流体转变的新型低温转变。参与这些研究的学生，从研究生到高中，都将获得基础物理和尖端技术方面的经验。他们将为工业、国家实验室和学术机构的科学研究和发展做出贡献。*技术摘要*这个项目的重点是使用液态氦研究氦的基本方面，以及利用氦的不同寻常的性质来探索凝聚态物理更广泛领域的重要问题。以前的研究将探索当3He和4He混合存在时，氦原子与弱结合基片，特别是固态氢原子之间的不寻常和无法解释的去耦合(除了Kosterlitz-Thouless去耦合)。这种脱钩现象表明了一种令人兴奋的可能性，即在这类薄膜中可能发生了一种不同于通常的超流体转变的新型低温转变。第二个焦点将是对存在无序状态下的氦膜的调查。第三，超流4He薄膜上的声波将被用来研究经典波在随机图案表面上的局域化。据预测，在氦膜中施加一个流场将改变局域化行为。这项研究的结果可能会对光学势中冷原子的物理研究以及光和信号处理在光子学领域的局部化产生潜在的影响。参与这项研究的学生，从高中到研究生，将获得基础物理和尖端技术方面的经验。他们将为工业、国家实验室和学术环境的科学研究和发展做出贡献。

****NON-TECHNICAL ABSTRACT****This project is focused on the use of liquid helium to study fundamental aspects of helium as well as using helium's unusual properties to explore important questions in the broader area of Condensed Matter Physics. Very thin films of helium become a friction-free superfluid at temperatures lower than about 456 degrees below zero Fahrenheit, and support waves, which act much like tiny tidal waves. Localization, a phenomenon in which waves are confined by a disordered environment, is a phenomenon of widespread importance. This importance reaches from the fundamental (the behavior of atoms in optical traps) to the applied, (the behavior of light in the technological areas of signal processing and the field of photonics). This project seeks experimental evidence for a change in the fundamental localization behavior of waves on a thin film of helium in a non-orderly environment when a direct flow of the fluid that supports the waves is applied. In another direction, earlier work has shown that when a thin film of the two kinds of helium atoms (the rare helium-3 and the more common helium-4) is atop a smooth solid hydrogen surface at low temperature there is an unexpected decoupling of atoms from the surface in addition to the usual superfluid decoupling. This suggests the exciting possibility that there may be a new type of low temperature transition that takes place in such films, different from the usual superfluid transition. The students, from graduate school down to high school, involved in these studies will gain experience in fundamental physics and cutting-edge technology. They will be poised to contribute to scientific research and development in industrial, national laboratory, and academic settings.****TECHNICAL ABSTRACT****This project is focused on the use of liquid helium to study fundamental aspects of helium as well as using helium's unusual properties to explore important questions in the broader area of Condensed Matter Physics. The former studies will probe the unusual and unexplained de-coupling of helium atoms (in addition to the Kosterlitz-Thouless decoupling) from a weak binding substrate, specifically solid hydrogen, when a mixture of 3He and 4He is present. This decoupling suggests the exciting possibility that there may be a new type of low temperature transition that takes place in such films, different from the usual superfluid transition. A second focus will be the investigation of helium films in the presence of disorder. Third sound waves on thin films of superfluid 4He will be used to study classical wave localization on randomly patterned surfaces. It is predicted that the imposition of a flow field in the helium film will change the localization behavior. The results of this study have a potential to impact the study of the physics of cold atoms in optical potentials and the localization of light and signal processing in the field of photonics. The students, from high school through graduate school, involved in this research will gain experience in fundamental physics and cutting-edge technology. They will be poised to contribute to scientific research and development in industrial, national laboratory, and academic settings.