Spin Filter with Polarized Superfluid: Effects of Surface and Interface

本文对铁磁超流体He-3的自旋流体动力学进行了实验研究。自旋极化的He-3为研究控制自旋输运、扩散和弛豫的基本过程提供了一个纯的、近乎理想的材料体系。早期的实验表明，磁性和非磁性流体He-3之间的“界面”可能为自旋弛豫提供新的通道。建议通过完全消除接口来提供对接口重要性的直接测试。提出了一种新的自旋过滤器实验，通过诱导铁磁流体流过“超漏”来产生比以往可能产生的更大的极化。本文将首次研究这种具有大非平衡极化的流体状态的流体力学和自旋动力学性质。实验将在高达15特斯拉的磁场下，将液态氦-3冷却至0.5开尔文。这些自旋流体动力学的研究与当前“自旋电子学”领域的研究密切相关。本研究具有宏观结构较简单、材料条件和参数改变相对容易、弛豫或退相干时间尺度较长等优点。拟议的工作将与东京大学固体物理研究所合作进行。研究生将参加国际合作研究。他们将获得超低温物理和材料物理方面的最新技术经验。他们将获得在工业，学术界或政府实验室的科学事业的坚实基础。本科生也将参与研究。这个项目旨在理解铁磁流体动力学的本质。当氦的同位素He-3被特别冷却到超低温时，铁磁流体状态就会发生。实验的动机是，当流体流过一个被称为自旋过滤器的小结构时，磁性流体的特性可能会发生新的变化。模型材料系统是铁磁液体He-3冷却到接近绝对零度：大约0.0005开尔文。此外，需要一个非常大的磁场，高达15特斯拉。这些“极端条件”只能在超低温实验室中使用。这项工作将通过涉及东京大学固体物理研究所的国际合作进行。铁磁氦-3之所以吸引人，是因为它是一种理想的纯物质，没有杂质，它的磁弛豫特性可以与更常见的或“自旋电子”材料相关。自旋流体动力学为利用电子的自旋自由度来承载信息的自旋电子学器件研究提供了一种新的模拟方法。因此，所提出的研究可能最终有助于自旋电子学器件技术。研究生参加国际合作研究，获得超低温物理和材料物理的最新技术经验。他们接受严格的培训，为他们在工业界、学术界或政府的职业生涯做好准备。本科生也将参与研究。

This research is focused on experimental investigations of the spin fluid dynamics in ferromagnetic superfluid He-3. The spin-polarized He-3 constitutes a pure, nearly ideal, material system for studying fundamental processes governing spin transport, diffusion and relaxation. Earlier experiments indicated that an "interface" between the magnetic and non-magnetic fluid He-3 could present a new channel for spin relaxation. It is proposed to provide a direct test of the importance of the interface by eliminating the interface altogether. A new spin filter experiment is proposed to create a much greater polarization than heretofore possible by inducing ferromagnetic fluid flows through a "superleak". The hydrodynamics and spin dynamics properties of such a fluid state with large non-equilibrium polarization will be studied for the first time. Experiments will be carried out with liquid He-3 cooled down to 0.5 mKelvin, in magnetic fields up to 15 Tesla. These studies of spin fluid dynamics are closely related to current research in the field of "spintronics". The proposed research has certain advantages, in that simpler macroscopic structures are involved, it is relatively easy to alter material conditions and parameters, and the relaxation or decoherence time scales are longer. The proposed work will be carried out in collaboration with the Institute for Solid State Physics of the Tokyo University. The graduate students will participate in international cooperative research. They will gain experience in the state-of-the-art technology in ultra low temperature physics and in materials physics. They will acquire a solid foundation for scientific careers in industry, academia or government laboratories. Undergraduate students will also participate in the research.This project is directed at understanding of the nature of ferromagnetic fluid dynamics. The ferromagnetic fluid state occurs when an isotope of helium, He-3, is specially cooled to ultralow temperatures. The motivation for the experiments is that novel changes in the magnetic fluid properties may occur when the fluid is made to flow through a small structure called a spin filter. The model material system is ferromagnetic liquid He-3 cooled to nearly absolute zero: about 0.0005 degrees Kelvin. In addition, a very large magnetic field, up to 15 Tesla, is required. These "extreme conditions" are only available in ultra low temperature laboratories. The work will be carried out via an international collaboration involving the Institute for Solid State Physics of the Tokyo University. The ferromagnetic He-3 is attractive because it is an ideal pure substance, free from impurities, and its magnetic relaxation properties can be related to more common or "spintronic" materials. The spin fluid dynamics provides a novel analog for spintronics device research where the spin degree of freedom of the electron is used to carry information. Hence the proposed research may ultimately contribute to spintronics device technology. The graduate students participate in international cooperative research and gain experience in the state-of-the-art technology in ultra low temperature physics and materials physics. They receive rigorous training that prepares them for careers in industry, academia or government. Undergraduate students will also participate in the research.