CAREER: Spectroscopic Exploration of Microscopic Superfluidity

该奖项的全部或部分资金来自《2021年美国救援计划法案》(公共法律117-2)。在化学系化学结构、动力学和机制(CSDM-A)计划的支持下，Paul Raston和他在詹姆斯·麦迪逊大学的研究团队将使用尖端的微波和激光光谱技术研究小分子与氦或氢的量子溶剂化。当液氦冷却到超低温时，它就变成了超流体，这是一种具有各种特殊性质的物质状态。这些特性之一是无摩擦流动的能力，这意味着如果孤立的超流体被设置为旋转，它将继续无限旋转。这种类型的无摩擦流动在大约80年前在块状超流氦中被发现，在大约20年前在微小的液滴(由大约10个氦原子组成)中被发现。令人惊讶的是，在微小液滴和大块液滴之间的超流性的演化在很大程度上仍然没有被探索。这一职业奖项支持使用最先进的光谱技术在这片未知领域进行好奇心驱动的探索。通过探索有限大小超流的新表现，这项工作旨在为理论提供新的挑战，并寻求在基础水平上对量子化学有更深的理解。该研究项目还将为本科生研究人员提供丰富的教育经验，并寻求吸引不同群体的学生进入科学领域。受新冠肺炎大流行期间在线学习困难的启发，该项目还包括一个教育部分，专注于开发虚拟仪器和实验，以便在无法亲自上课或无法使用仪器的情况下向本科生讲授光谱学的现代技术和方法。这项工作的一个关键智力贡献在于根据朗道标准确定超流所需的最小氦原子数量，朗道标准是体超流性的传统标准。这个数字特别重要，因为它对应于从具有离散能级的星团向具有(准)连续能级的星团的转变，这意味着小星团的能量性质与整体之间的差距(最终)已经弥合。在此过程中，预计转动惯量将发生广泛的振荡，这被认为与溶剂化壳层的打开和关闭有关，从而提供了关于微观溶剂化的详细结构信息。另一项重大贡献涉及通过研究小分子芳烃与氦的量子溶剂化来探索纳米表面是如何润湿的。这些系统的光谱提供了关于氦流体如何覆盖表面的信息，以及关于超流体行为如何随着星团大小而演变的信息。最后，拉斯顿博士和他的研究团队正在研究费米子(氢化氢)的量子溶剂化作用，以实验测试之前报道的玻色子(氦或氢)密度与分子旋转的解耦是否真的是微观超流的指标。这个项目的教育层面的灵感来自于在网上提供高级实验室课程的相关困难。为了帮助缓解这些挑战，并使那些无法获得所需科学仪器的人有可能进行实验，正在开发一套现代虚拟仪器。用户友好的界面旨在让学生参与并指导他们完成各种实验，这些实验将在网络上免费提供，以便用户可以轻松访问。虚拟仪器将提供一个在自主环境中学习数据采集的平台，同时还将促进对仪器控制的更好理解，并培养学生对仪器操作的直觉。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

This award is funded in whole or in part under the American Rescue Plan Act of 2021 (Public Law 117-2).With support from the Chemical Structure, Dynamics, and Mechanisms-A (CSDM-A) Program in the Division of Chemistry, Paul Raston and his research team at James Madison University will investigate the quantum solvation of small molecules with helium or hydrogen using sophisticated microwave and laser spectroscopy techniques. When liquid helium is cooled to ultra-low temperatures it becomes superfluid, which is a state of matter that is characterized by a variety of peculiar properties. One of these properties is the ability to flow without friction, which implies that if an isolated superfluid is set into rotation, it will continue to rotate indefinitely. This type of frictionless flow was discovered in bulk superfluid helium about 80 years ago, and in tiny droplets (consisting of about 10 helium atoms) about 20 years ago. Surprisingly, the evolution of superfluidity in the realm between tiny droplets and the bulk remains largely unexplored. This CAREER award supports curiosity-driven exploration in this uncharted territory using state-of-the-art spectroscopic techniques. By exploring new manifestations of finite-sized superfluidity, the work aims to provide fresh challenges for theory and seeks to provide for a deeper understanding of quantum chemistry at a fundamental level. The research program also will provide an enriching educational experience for undergraduate student researchers and seeks to attract a diverse body of students into science. Inspired by difficulties associated with online learning during the COVID-19 pandemic, the project also includes an educational component that focuses on developing virtual instrumentation and experiments for teaching modern techniques and approaches in spectroscopy to undergraduate students when in-person classes are not possible, or when the instrumentation is not available.A key intellectual contribution of this work lies in determining the minimum number of helium atoms that are required for superfluidity according to the Landau criterion, which is the traditional criterion for bulk superfluidity. This number is especially important since it corresponds to the transition from the cluster having discrete energy levels to one that has a (quasi) continuum of energy levels, implying that the gap between the energetic properties of small clusters and the bulk has (finally) been bridged. Along the way, it is expected that broad oscillations in the rotational inertia will occur, which are thought to be related to the opening and closing of solvation shells, thus providing detailed structural information regarding microscopic solvation. Another significant contribution involves exploring how nanoscopic surfaces are wetted by investigating the quantum solvation of small aromatics with helium. The spectra of these systems provide information about how the helium fluid coats the surfaces, and about how the superfluid behavior evolves with cluster size. Finally, Dr. Raston and his research team are investigating quantum solvation by fermions (deuterium hydride) in order to experimentally test whether the previously reported decoupling of boson (helium or hydrogen) density from molecular rotation is indeed an indicator of microscopic superfluidity. The educational dimension of this project is inspired by the difficulties associated with delivering upper-division laboratory courses online. To help alleviate these challenges and to make experiments possible for those who do not have access to the required scientific instrumentation, a suite of modern virtual instruments is being developed. The user-friendly interface is designed to engage and guide students through a variety of experiments that will be made freely available on the web so that users can easily access them. The virtual instruments will provide a platform for learning about data acquisition in an autonomous environment, while also fostering an improved understanding of instrument control and developing student intuition about instrument operation.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.