Collective Mode Studies in Superfluid Fermi Systems

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w:\awards\awards96\*.doc 96-23682 Ketterson External dynamic probes with frequencies of the order of the energy gap will be used to study the excitation spectrum of the unconventional superfluids Helium-3 and UPt3. The probes will be microwaves and ultrasound for UPt3, and an oscillating magnetic field and ultrasound for Helium-3. The temperature dependence of the microwave impedance of Upt3 will be studied using a recently developed variable-frequency, cryogenic, microwave spectrometer. This will allow determination of the temperature-dependent energy gap and will enable a search for collective modes in this material. Helium-3 shear waves and their interaction with collective modes will be investigated using a unique variable- path-length sound cell developed in this laboratory. Finally, a search will be performed for evidence of interaction between an oscillating magnetic field and various collective modes in Helium- 3. %%% Superconductivity is finding on increasing number of applications, including high-field magnets, sensitive magnetic- field detectors and high-speed computers. Most of the present interest surrounds the high-temperature superconductors. These materials, which may be referred to as unconventional superconductors, are thought to derive their properties from mechanisms that differ from those found in conventional superconductors. Two other classes of materials also show unconventional behavior: the rare isotope of helium (Helium-3) and a uranium-platinum compound (UPt3). These materials are of unique scientific interest as well as being testing grounds for developing an understanding of other non-conventional superconductors (including the high-Tc materials). This project will employ high-frequency probes, including microwaves and ultrasound, to study excitation phenomena in these mat erials and thence derive an understanding of the unconventional nature of their superconductivity and superfluidity ***