Electronic and Magnetic Phenomena in Transition Metal Oxides and Hybrid Ferromagnet/Superconductor Nanostructures

****非技术摘要****凝聚态物理中的两个主要主题是量子临界现象和非常规超导性。当量子物质变得不稳定到一个新的有序基态时，就会发生量子相变。因此，量子临界是一个概念，描述了由温度以外的外部参数（如化学成分、压力或磁场）驱动的竞争基态之间的相变。原则上，相变发生在绝对零度。然而，越来越多的实验工作表明，在有限的温度下，从根本上讲，新的物理学可以在广泛的区域内发展。本研究项目的目标是增强我们对量子临界控制非常规超导体有限温度特性的程度的基本理解，并为非常规超导性和磁性之间的相互作用提供见解。这些基础研究的结果有望进一步了解磁性和超导性之间的相互作用，并促进电子传感器和设备（如磁场传感器）甚至计算机逻辑设备的应用。这个高度跨学科的项目将使研究生和博士后受益于接触各种重要的实验技术和各种不同的物理系统和现象。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。****技术摘要****该个人研究者奖支持一个研究项目，该项目涉及凝聚态物理的主要主题：铁镍中的量子临界性和非常规超导性，以及铁镍和铁磁体/超导体（F-S）混合结构中超导性和磁性之间的相互作用。这些研究有望显著增强我们对量子临界控制非常规超导体有限温度特性的基本理解，并有望更深入地了解非常规超导性和磁性之间的相互作用。此外，通过比较和对比铁镍和铜酸盐超导体，该项目可能有助于揭示理论家解决高温超导之谜所需的重要线索。非均相F-S结构的铁磁子系统和超导子系统之间的强相互作用不会抑制其中任何一种性质，而是会极大地改变两者的结构和性质。因此，这些结构为新的科学技术提供了无限的可能性。例如，这种结构为传输特性可以通过相对较弱的磁场轻松调谐的器件提供了重要的技术前景。这个高度跨学科的项目将使研究生和博士后受益于接触各种重要的实验技术和各种不同的物理系统和现象。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。

****NON-TECHNICAL ABSTRACT****Two major themes in condensed matter physics are quantum critical phenomena and unconventional superconductivity. A quantum phase transition takes place when quantum matter becomes unstable to a new, ordered ground state. Therefore, quantum criticality is a concept that describes a phase transition between competing ground states driven by an external parameter other than temperature such as chemical composition, pressure, or magnetic field. In principle the phase transition takes place at absolute zero. Nevertheless, a growing body of experimental work indicates that fundamentally new physics can develop over a wide region at finite temperatures. The goal of this research project is to enhance our fundamental understanding of the extent to which quantum criticality controls the finite temperature properties of unconventional superconductors and provide insight into the mutual interplay between unconventional superconductivity and magnetism. The results from these basic investigations are expected to provide further understanding of the interplay between magnetism and superconductivity and to facilitate applications to electronic sensors and devices such as magnetic field sensors or even computer logic devices. This highly interdisciplinary project will allow graduate students and postdocs to benefit from exposure to a diversity of important experimental techniques and a variety of different physical systems and phenomena. 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.****TECHNICAL ABSTRACT****This individual investigator award supports a research project addressing major themes in condensed matter physics: quantum criticality and unconventional superconductivity in Fe pnictides, and the interplay between superconductivity and magnetism in pnictides and hybrid ferromagnet/superconductor (F-S) structures. These studies are expected to significantly enhance our fundamental understanding of the extent to which quantum criticality controls the finite temperature properties of unconventional superconductors and promise a deeper insight into the mutual interplay between unconventional superconductivity and magnetism. In addition by comparing and contrasting the Fe-pnictides and cuprates superconductors, the project may contribute to uncovering the vital clues that theorists need to solve the mystery of high-temperature superconductivity. The strong mutual interaction between the ferromagnetic and superconducting subsystems of heterogeneous F-S structures does not suppress either property, but rather can dramatically change the structure and properties of both of them. Therefore these structures offer unlimited possibilities for qualitatively new science and technologies. For example, such structures offer important technological promise for devices whose transport properties can be easily tuned by comparatively weak magnetic fields. This highly interdisciplinary project will allow graduate students and postdocs to benefit from exposure to a diversity of important experimental techniques and a variety of different physical systems and phenomena. 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.