Collective Mode Studies in Superfluid Fermi Systems

我们将使用频率为能隙数量级的外部动态探头来研究非常规超流体氦-3和UPt3的激发光谱。UPt3的探头是微波和超声波，氦-3的探头是振荡磁场和超声波。利用最新研制的变频低温微波光谱仪将研究UPT3的微波阻抗与温度的关系。这将允许确定依赖于温度的能隙，并将使在这种材料中搜索集体模式成为可能。氦-3横波及其与集体模的相互作用将利用本实验室开发的独特的可变路径长度的声室来研究。最后，我们将在氦-3中寻找振荡磁场和各种集体模相互作用的证据。超导电性随着越来越多的应用而被发现，包括高场磁铁、灵敏磁场探测器和高速计算机。目前人们的兴趣主要集中在高温超导体上。这些材料可能被称为非传统超导体，它们的性质被认为是从不同于传统超导体的机制中获得的。另外两类材料也表现出非常规行为：稀有的氦同位素(氦-3)和铀-铂化合物(UPt3)。这些材料具有独特的科学价值，也是了解其他非常规超导体(包括高温超导材料)的试验场。这个项目将使用高频探头，包括微波和超声波，来研究这些材料中的激发现象，从而了解它们的超导性和超流性的非常规性质*

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 ***