Helium Films: Localization and Transitions

University Of Massachusetts Amherst, Amherst MA

Investigators

Abstract

****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.