Vortices and the Interplay between Superconductivity and Magnetism

涡旋以及超导性和磁性之间的相互作用

• 批准号: 0804887
• 负责人: Morten Eskildsen
• 金额: $ 44万
• 依托单位: University of Notre Dame
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2008
• 资助国家: 美国
• 起止时间: 2008-07-01 至 2014-06-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0804887&HistoricalAwards=false
• 关键词: Vortices; Interplay; between; Superconductivity; Magnetism

NON-TECHNICAL ABSTRACTWhen a superconductor is placed in a magnetic field, it is threaded by swirling whirlpools of electric current known as vortices or flux-lines. Besides being a fundamental limiting factor in the practical applications of superconductors, the vortices also provide a unique probe into the microscopic properties of the host superconductor. While it is know that superconductivity always arises due to the binding of electrons into so-called Cooper pairs, the way in which this binding occurs is still essentially unknown in many classes of materials including most notably the high-temperature oxides. The main goal of the present project is to investigate a particular electron pairing in what is known as the Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) state which was predicted theoretically more than 40 years ago but has so far eluded direct observation. While studies of the FFLO phase in itself are fundamental in nature, the larger framework of interplay between magnetism and superconductivity is of relevance for the practical applications of superconductivity. Students participating in the project will be trained in the use of neutron scattering and thereby the project will increase the future user base for US neutron sources such as the new constructed spallation neutron source at the Oak Ridge National Laboratory. To enhance broader awareness of the potential applications of superconductivity a demonstration experiment featuring superconducting levitation will be constructed. This will allow participants to lay down a magnetic track, and levitate a model train containing a high-temperature superconductor cooled with liquid nitrogen.TECHNICAL ABSTRACTVortices induced in a superconductor by an applied magnetic field can serve as microscopic probes of the detailed nature of the superconducting state in the host material. The main focus of this project is to use vortex studies to investigate the interplay between paramagnetism and superconductivity, both in materials with localized magnetic moments as well as in the heavy-fermion superconductor CeCoIn5. Of particular interest is the possible ways in which pairing of electrons can occur, and the theoretical prediction of a non uniform so-called Fulde-Ferrell-Larkin-Ovcninnikov (FFLO) superconducting state in systems where the upper critical field is strongly Pauli limited. Recently there has been mounting experimental evidence for the existence of such a FFLO phase in CeCoIn5, but to date no structural evidence for this state has been observed in this or any other superconductor; the detailed properties of the FFLO state are still effectively unknown. The principal aim of this project is to provide such direct evidence for the FFLO state in CeCoIn5 (if it exists) by small-angle neutron scattering of the vortex lattice complemented with scanning tunnelling spectroscopy. The project incorporates substantial participation by undergraduate and graduate students and exposes them to research at large international facilities. Hence the project contributes to the education and training of a new generation of scientists with expertise in fields of high demand. Finally, a demonstration experiment featuring high-temperature superconducting levitation will be developed for use in outreach activities.

当超导体被置于磁场中时，它被称为涡旋或磁通线的漩涡电流缠绕。除了是超导体实际应用中的一个基本限制因素外，涡旋还为研究宿主超导体的微观性质提供了一个独特的探针。虽然众所周知，超导电性总是由于电子与所谓的库珀对的结合而产生，但在许多类型的材料中，这种结合发生的方式基本上仍然是未知的，包括最明显的高温氧化物。本项目的主要目标是研究一种特殊的电子配对，这种电子配对被称为Fulde-Ferrell-Larkin-Ovchinnikov(FFLO)态，40多年前从理论上预测了这种态，但到目前为止一直没有直接观察到这种态。虽然对FFLO相本身的研究在本质上是基础的，但磁性和超导电性之间的相互作用的更大框架与超导电性的实际应用有关。参加该项目的学生将接受使用中子散射的培训，因此该项目将增加美国中子源的未来用户基础，例如橡树岭国家实验室新建造的散裂中子源。为了提高人们对超导潜在应用的认识，将建造一个以超导悬浮为特色的示范实验。这将允许参与者铺设一条磁道，并将包含用液态氮冷却的高温超导体的模型列车悬浮起来。技术简介外加磁场在超导体中感应的涡流可以作为微观探测器，了解宿主材料中超导状态的详细性质。这个项目的主要焦点是利用涡旋研究来研究顺磁性和超导电性之间的相互作用，无论是在具有局域磁矩的材料中，还是在重费米子超导体CeCoIn5中。特别令人感兴趣的是电子配对发生的可能方式，以及在上临界场强烈受限的系统中对非均匀所谓的Fulde-Ferrell-Larkin-Ovcinenikov(FFLO)超导态的理论预测。最近有越来越多的实验证据表明CeCoIn5中存在这样的FFLO相，但到目前为止，还没有在这个或任何其他超导体中观察到这种状态的结构证据；FFLO态的详细性质实际上仍然是未知的。这个项目的主要目的是通过涡旋晶格的小角中子散射和扫描隧道光谱的补充，为CeCoIn5(如果存在)中的FFLO态提供这样的直接证据。该项目吸收了本科生和研究生的大量参与，并使他们有机会在大型国际设施中进行研究。因此，该项目有助于教育和培训在高需求领域具有专门知识的新一代科学家。最后，将开发一个以高温超导悬浮为特色的演示实验，用于推广活动。