Electronic and Magnetic Phenomena in Iron-based Superconductors

非技术描述：凝聚态物理的两个主要主题是量子临界现象和非常规超导电性。量子相变在零温度下发生，描述了由外部参数(如化学成分、压力或磁场)驱动的竞争基态之间的相变。最近对非常规超导体的研究表明，超导电性在磁有序相附近发展。这增加了这些系统中量子相变的可能性，这些相变是由竞争类型的这种顺序引起的。目前对铁基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制的了解上。这些研究加强了我们对量子相变在多大程度上控制这些超导体的有限温度性质的基本理解，并有望深入了解超导和磁性之间的相互作用。它们还可以提供其他非传统超导体的线索，如铜酸盐，并有助于在全球范围内更好地理解高温超导这一新现象。这个高度跨学科的项目允许研究生和本科生、博士后和来访者从接触各种实验技术、各种不同的物理系统和现象以及凝聚态物理的前沿话题中受益。该研究项目参与者获得的专业知识的多样性是当今以知识为基础、技术驱动的经济中的一大优势，对未来在工业、政府或学术界的职业生涯有利。为博士后和研究生提供专业指导。一名女性博士生参与了这个项目，因此，该项目增加了该领域的多样性。与罗马尼亚和中国科学家的国际合作为罗马尼亚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，以实验方式验证在量子力学中学到的违反直觉的物理现象。她还通过开发新的物理和生命科学研究生课程中的物理科学部分，解决了6-10年级科学教师的专业发展需求。最后，她为初中和高中物理教师和他们的学生提供工作坊和实验室参观。技术描述：这项提议涉及凝聚态物理中的一个主要主题：铁基超导体中的非传统超导电性。这项研究极大地提高了我们对铁锂辉石/硫化物的电荷传导和磁性的基本认识，解决了与磁性和超导电性相互作用有关的问题，并有助于更全面地理解高温超导这一新现象。本研究的目的是：(1)研究具有反铁磁Mott绝缘体或反铁磁自旋密度波母体的铁锡/硫化物超导体中具有实空间织构的新型电子量子态；(2)揭示反铁磁性和超导电性的微观共存及其随掺杂的演化；(3)研究量子临界性，以揭示由控制参数引起的可能的量子相变，阐明超导态中顺磁和反铁磁相之间的相界，并生成为超导相中的量子临界线提供直接证据的相图；(4)研究超导带隙的对称性，以便毫不含糊地区分不同的配对对称性，揭示带隙对兴奋剂依赖的任何普遍性；(5)揭示伪带隙区域的起源；(6)通过全面和多方面的研究促进高素质人员的培训，通过6-10年级的教育者发展改善STEM教育，并开展外联活动。这些研究中使用的方法有电阻率、磁阻、电流-电压、扭矩和磁化强度测量。了解这些复杂材料中固有的电子、磁和磁传输机制可能是了解它们独特的和潜在有用的物理性质的关键组成部分。通过铁镍矿/硫化物和铜酸盐的比较和对比，拟议中的研究可能有助于最终揭开理论家解开高温超导之谜所需的关键线索。更广泛地说，这些基础研究的结果有助于进一步了解其他非传统超导体的磁性和超导电性之间的相互作用，并深入了解适当的掺杂方案，以促进电子传感器和设备的应用。

Nontechnical description: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 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 mutual interplay between superconductivity and magnetism. They could also offer clues about other unconventional superconductors, such as the cuprates, and contribute to a more global understanding of the novel phenomenon of high temperature superconductivity. This highly interdisciplinary project allows graduate and undergraduate students, postdocs, and visitors 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 postdoc and graduate students. A female Ph.D. student participates in this project, hence, the project increases diversity within the field. The international collaborations with scientists in Romania and 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. She also addresses the professional development needs of science teachers in grades 6-10 by developing the physical science component of a new physical and life science graduate course. Finally, she provides middle school and high school physics teachers and their students workshops and lab tours. Technical description:This proposal addresses a major theme in condensed matter physics: unconventional superconductivity in Fe-based superconductors. The proposed research significantly enhances our fundamental understanding of charge conduction and magnetism of 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 novel electronic quantum states with real-space texture in iron pnictides/chalcogenites superconductors with either an antiferromagnetic Mott insulator or antiferromagnetic spin density wave parent compound; (2) reveal the microscopic coexistence of antiferromagnetism and superconductivity and its evolution with doping; (3) study quantum criticality in order to reveal possible quantum phase transitions induced by control parameters, elucidate the phase boundary between the paramagnetic and antiferromagnetic phases inside the superconducting state, and generate a phase diagram that provides direct evidence for a quantum critical line inside the superconducting phase; (4) study the symmetry of the superconducting gap in order to unambiguously distinguish between different pairing symmetries and reveal any universality in the doping dependence of the gap; (5) reveal the origin of the pseudogap region; (6) facilitate the training of highly qualified personnel through comprehensive and multifaceted research, improve STEM education through educator development at 6-10 grade levels, and perform outreach activities. The methods that are used in these studies are resistivity, magnetoresistivity, current-voltage, torque, and magnetization measurements. Understanding the intrinsic electronic, magnetic, and magnetotransport mechanisms in these complex materials may be a key component in understanding their unique and potentially useful physical properties. With iron pnictides/chalcogenites and cuprates to compare and contrast, the proposed research could contribute to finally uncovering the vital clues that theorists need to solve the mystery of high-temperature superconductivity. More broadly, the results from these basic investigations provide further understanding of the interplay between magnetism and superconductivity of other unconventional superconductors and insight into appropriate doping schemes to facilitate applications to electronic sensors and devices.