Electronic and Magnetic Phenomena in Heavy-Fermion and Iron-Based Superconductors

摘要：凝聚态物理的两大主题是量子临界现象和非常规超导性。量子相变发生在零温度下，描述了由外部参数（如化学成分、压力或磁场）驱动的相互竞争的基态之间的相变。最近对非常规超导体的研究表明，超导性是在磁性有序相附近发展起来的。这提高了这些系统中量子相变的可能性，这些相变是由这些顺序的竞争类型引起的。目前对重费米子和铁基超导体等非常规超导体的研究主要集中在对这些超导体的正常态性质和超导机理的认识上。这些研究增强了我们对量子相变控制这些超导体有限温度特性的程度的基本理解，并有望深入了解其他非常规超导体的磁性和超导性之间的相互作用。这种新知识可以提供对非常规SC现象的更全面的理解。这个高度跨学科的项目使研究生和本科生受益于接触多种实验技术，各种不同的物理系统和现象，以及凝聚态物理学的前沿主题。在当今以知识为基础、技术驱动的经济中，本研究项目参与者所获得的专业知识的多样性是一个巨大的优势，对未来在工业、政府或学术界的职业生涯有益。为研究生提供专业指导。与中国科学家的国际合作为中国的研究和教育基础设施做出了贡献。首席研究员为高级实验室开发教学实验室模块，通过实验验证量子力学中所学到的反直觉物理现象；例如，单个光子如何干涉自身，或者局部实在性如何被违反。她还参与了K-12学生的STEM教育，参与了一些活动：年度STEM项目博览会、科学体验实习和青年女性暑期学院。此外，她还为初高中学生和他们的物理老师提供研讨会和实验室参观。技术摘要：本提案解决了凝聚态物理中的一个主要主题：重费米子和铁基超导体中的量子临界现象。本研究将大大提高我们对重费米子和铁镍酸盐/硫原岩的电荷传导和磁性的基本认识，解决磁性与超导性相互作用的相关问题，并有助于对高温超导的新现象有更全面的认识。本研究的目的是：(1)研究反铁磁性和超导性的共存；(2)揭示量子相变；(3)研究量子临界点的性质；(4)研究赝隙区域，寻找向列态；(5)通过全面和多方面的研究促进高素质人才的培养，改善K-12 STEM教育。在这些研究中使用的方法是电阻率、磁电阻率、电流电压、扭矩、热电功率和磁化测量。提出的研究将大大提高我们对量子临界现象的基本理解，这些现象是由铁基超导体和重费米子超导体中相互竞争的顺序引起的。具体来说，它将解决与磁性和超导性之间相互作用相关的问题，并揭示基态的本质，例如，如果没有超导性的干预，传统金属或有序相就会出现。从根本上说，它将揭示量子临界控制这些系统的有限温度特性的程度。这项研究也有助于对非常规超导的新现象有更全面的了解。了解这些复杂材料的内在电子、磁性和磁输运机制对于理解强相关材料的本质和揭示非常规超导性的起源至关重要。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

Non-Technical Abstract:Two major themes in condensed matter physics are quantum critical phenomena and unconventional superconductivity. A quantum phase transition takes place at zero temperature and describes a phase transition between competing ground states driven by an external parameter such as chemical composition, pressure, or magnetic field. The recent studies of unconventional superconductors show that superconductivity develops in proximity to a magnetically ordered phase. This raises the possibility of quantum phase transitions in these systems arising from competing types of such orders. The present studies of unconventional superconductors such as heavy fermions and iron-based superconductors mainly focus on the understanding of the normal state properties of these superconductors and on the mechanism of superconductivity. These studies enhance our fundamental understanding of the extent to which a quantum phase transition controls the finite temperature properties of these superconductors and promise insight into the interplay between magnetism and superconductivity of other unconventional superconductors. This new knowledge could provide a more global understanding of the phenomenon of unconventional SC. This highly interdisciplinary project allows graduate and undergraduate students to benefit from exposure to a diversity of experimental techniques, a variety of different physical systems and phenomena, and forefront topics in condensed matter physics. The diversity of the expertise gained by the participants in this research program is a substantial advantage in today's knowledge based, technology driven economy, being beneficial to a future career in industry, government, or academia. Professional mentoring is provided for the graduate students. The international collaborations with scientists in China contribute to the nation's infrastructure for research and education. The principal investigator develops teaching lab modules for a senior laboratory that verifies experimentally counterintuitive physical phenomena learned in Quantum Mechanics; e.g., how a single photon will interfere with itself, or how local realism can be violated. She also participates in the STEM education of K-12 students by contributing to several activities: Annual STEM Project Fair, Science Experience Internship, and Young Women's Summer Institute. In addition, she provides middle school and high school students and their physics teachers workshops and lab tours. Technical Abstract:This proposal addresses a major theme in condensed matter physics: quantum critical phenomena in heavy fermions and iron-based superconductors. The proposed research significantly enhances our fundamental understanding of charge conduction and magnetism of heavy fermions and iron pnictides/chalcogenites, addresses issues related with the interplay between magnetism and superconductivity, and contributes to a more global understanding of the novel phenomenon of high temperature superconductivity. The goals of this research are to: (1) study coexistence of antiferromagnetism and superconductivity; (2) reveal quantum phase transitions; (3) study nature of quantum critical points; (4) study pseudogap region and search for nematic states; (5) facilitate the training of highly qualified personnel through comprehensive and multifaceted research and improve K-12 STEM education. The methods that are used in these studies are resistivity, magnetoresistivity, current-voltage, torque, thermoelectric power, and magnetization measurements. The proposed research will significantly enhance our fundamental understanding of quantum critical phenomena, arising from competing types of orders, in iron-based and heavy-fermion superconductors. Specifically, it will address issues related with the interplay between magnetism and superconductivity, and reveal the nature of the ground state, for example a conventional metal or an ordered phase, which would have appeared had superconductivity not intervened. Fundamentally, it will reveal the extent to which quantum criticality controls the finite temperature properties of these systems. This research could also contribute to a more global understanding of the novel phenomenon of unconventional superconductivity. Understanding the intrinsic electronic, magnetic, and magnetotransport mechanisms in these complex materials is critical to understanding the nature of strongly correlated materials and revealing the origin of unconventional superconductivity.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.