Spin Filter with Polarized Superfluid: Effects of Surface and Interface

本研究致力于铁磁超流He-3自旋流体动力学的实验研究。自旋极化的He-3构成了一个纯粹的、近乎理想的材料系统，用于研究控制自旋输运、扩散和弛豫的基本过程。早期的实验表明，磁性流体He-3和非磁性流体He-3之间的“界面”可能为自旋弛豫提供了一个新的通道。建议通过完全取消接口来提供对接口重要性的直接测试。一项新的自旋过滤实验被提出，它通过诱导铁磁流体流过“超级泄漏”来产生比目前可能的更大的极化。首次研究了这种具有大的非平衡极化的流体状态的流体动力学和自旋动力学性质。实验将在液体He-3冷却到0.5mKelvin，磁场高达15特斯拉的情况下进行。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。所提出的研究具有一定的优势，因为它涉及更简单的宏观结构，相对容易改变物质条件和参数，并且弛豫或退相干时间尺度较长。拟议的工作将与东京大学固体物理研究所合作开展。研究生将参加国际合作研究。他们将在超低温物理和材料物理方面获得最先进的技术经验。他们将为在工业、学术界或政府实验室的科学生涯奠定坚实的基础。本科生也将参与这项研究。本项目旨在了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度时，就会出现铁磁流体状态。这些实验的动机是，当流体流经一种名为自旋过滤器的小结构时，磁性液体的性质可能会发生新的变化。模型材料系统是铁磁性液体He-3，冷却到接近绝对零度：大约0.0005开尔文。此外，还需要非常大的磁场，最高可达15特斯拉。只有在超低温实验室中才能找到这些“极端条件”。这项工作将通过东京大学固体物理研究所参与的国际合作进行。铁磁性He-3之所以吸引人，是因为它是一种理想的纯物质，不含杂质，其磁弛豫特性可以与更常见的或更多的自旋电子材料有关。自旋流体动力学为电子自旋自由度用于携带信息的自旋电子器件的研究提供了一种新的模拟方法。因此，拟议的研究可能最终有助于自旋电子器件技术。研究生参与国际合作研究，积累了超低温物理和材料物理的最新技术经验。他们接受了严格的培训，为他们在工业、学术界或政府的职业生涯做好准备。本科生也将参与这项研究。

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.