Acoustic Birefringence and Superfluid 3He

Northwestern University, Evanston IL

Investigators

Abstract

This project will further our understanding of a broad class of materials of considerable interest and importance to a wide range of scientific disciplines including quantum fluids and materials physics. The main goal is to develop new acoustic techniques based on the discovery of the Acoustic Faraday Effect, a discovery made last year of an effect strictly analogous to the important magneto-optic effect discovered by Michael Faraday in 1845. The proposed research will improve the spectroscopy of order parameter modes in superfluid 3He by several orders of magnitude using the techniques based on these acoustic principles. These experiments will give new and important information on the nature of the superfluid itself as well as on the pairing mechanisms that give rise to it. New collective modes of the superfluid will be sought which have been predicted theoretically and which can be identified from the new experimental methods. A second goal of the proposed work is to study impurity scattering effects which can suppress superfluidity in 3He. This will give important insight into the unusual superfluid behavior in 3He and suggest how to control the superfluid suppression. New phases and unusual properties have recently been discovered but which are not consistent with present theoretical understanding. To pave the way for better use of superconductivity as well as superfluidity it is very important to gain this understanding in 3He using impurities introduced into 3He in a controlled manner by means of very porous silica aerogel. Undergraduate students, graduate students, and some high school projects will be part of this research. Two local high school students are planning to prepare projects for the national Intel competition based on their experience in this low temperature laboratory. The integration of supervision from faculty, postdoctoral associates, and graduate students with these projects is a unique and mutually beneficial experience. %%% The proposed research will develop understanding of an important class of materials holding significant promise for applications to our society and for basic scientific knowledge. They are called unconventional quantum systems. This class includes superconducting materials for which their successful application requires development of new measurement tools. The main goal of the project is to develop a new acoustic spectroscopy using techniques similar to optical techniques that have been so important in the past 50 years in the semiconductor-materials field. The proposed research will improve the spectroscopy of order parameter collective modes in superfluid 3He by several orders of magnitude using the new acoustic principles. The experiments will reveal the nature of the superfluid and the physical mechanisms responsible for it. Since this material is an excellent representative of all materials in this important class it can be expected that there will be broad impact on their applications resulting from the proposed work. A second goal is to determine the sensitivity to impurities of the superconducting and superfluid behaviors. The results will pave the way for better use of superconductivity. Undergraduate students, graduate students, and some high school projects will be part of this research. Two local high school students are planning to prepare projects for the national Intel competition based on their experience in the university laboratory. The integration of research activity from faculty, postdoctoral associates, and graduate students with these high school projects will be a unique and mutually beneficial experience.