CAREER: Spectroscopic Exploration of Microscopic Superfluidity

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.