Impurity Effects in Superfluid Helium Three

超流氦三中的杂质效应

• 批准号: 9703575
• 负责人: William Halperin
• 金额: $ 33万
• 依托单位: Northwestern University
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 1997
• 资助国家: 美国
• 起止时间: 1997-08-15 至 2000-07-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=9703575&HistoricalAwards=false
• 关键词: Impurity; Effects; Superfluid; Helium; Three

9703575 Halperin High resolution nuclear resonance (NMR) experiments on helium 3 are proposed in order to study the normal and superfuid helium 3 states. Temperature dependent NMR frequency shifts in the normal state will be investigated as a function of magnetic field in order to identify their origin which appears to be of fundamental significance. High resolution NMR experiments and heat capacity measurements will be performed on superfluid helium 3 aerogels to understand the effects of impurities introduced by the aerogel into this important superfluid system. Close interaction with theoretical work should allow us to establish the extent to which anisotropic scattering models can account for our observations. The basic tools that we propose to use are low temperature nuclear demagnetization techniques to prepare samples of helium 3 imbibed into highly porous silica aerogel. The transition to superfluidity and the strength of the order parameter and energy gap will be determined mainly by nuclear magnetic resoncnce methods, complemented by acoustic excitation of order parameter collective modes, thermal conductivity, and heat capacity measurements. %%% The proposed work will further our understanding of a broad class of materials of considerable interest in condensed matter physics and of importance to a wide range of applications involving superconductivity. The study of impurity effects on the suppression of the transition temperature for superfluidity in helium 3 will give important insight into the unusual superfluid behavior in helium 3 as well as for other similar Superconducting systems. New phases and unusual properties concerning the impurity helium 3 problem have recently been discovered by several groups including our own at Northwestern. The impurities can be introduced in the helium 3 using very dilute aerogel. The aerogel consists of tenuous strands of silica polymer of very high porosity. The helium 3 impurity problem is a model for un derstanding the limitations and basic properties of new classes of superconducting materials including high temperature superconductors. The proposed work is also relevant to the behavior of neutron matter in the cores of neutron stars. These systems all have the common important characteristic of spontaneously broken symmetries beyond gauge symmetry which is itself responsible for the superfluid behavior. As such they are all extremely sensitive to impurity effects which must be investigated if the basic behavior of these systems is to be understood and if the potential for their application is to be realized. This situation is particularly relevant to the case of the high temperature superconductors for which the proposed work can be viewed as a paradigm. ***

提出了9703575 HALPERIN高分辨率核共振（NMR）实验，以研究正常和超法氦3状态。 正常状态下的温度依赖性NMR频率转移将作为磁场的函数研究，以识别其起源，这似乎具有基本意义。 高分辨率的NMR实验和热容量测量将在超流体氦3 Aerogels上进行，以了解气凝胶引入的杂质的影响。 与理论工作的密切相互作用应该使我们能够确定各向异性散射模型可以解释我们的观察结果的程度。 我们建议使用的基本工具是低温核电磁化技术，以准备氦3样品中吸收到高度多孔的二氧化硅气凝胶中。 向超流体的过渡以及顺序参数和能量差距的强度将主要由核磁共振方法决定，并通过订单参数集体模式的声激发，导热率和热容量测量值进行补充。 %% %%拟议的工作将进一步理解对凝结物理学有相当兴趣的广泛材料的理解，并且对于涉及超导性的广泛应用非常重要。 杂质的研究对氦3中超流体抑制的抑制作用将使人们对氦3中异常的超流体行为以及其他类似的超导系统具有重要的见解。 最近，包括我们自己在西北地区在内的几个小组发现了有关杂质氦3问题的新阶段和异常属性。 可以使用非常稀释的气凝胶在氦3中引入杂质。 气凝胶由非常高的孔隙率的硅胶聚合物组成。 氦3杂质问题是一个模型，以阐明新的超导材料（包括高温超导体）的局限性和基本特性。 所提出的工作也与中子恒星核心中的中子物质的行为有关。 这些系统都具有自发损坏的对称对称性超出规格对称性的共同重要特征，这本身就是造成超流体行为的原因。 因此，如果要理解这些系统的基本行为，并且是否要实现其应用的潜力，则必须对杂质效应极为敏感。 这种情况与高温超导体的情况尤其重要，可以将拟议的工作视为范式。 ***