Low Energy Spectroscopy of Complex, Geometrically Frustrated and Strongly Correlated Matter

非技术：光谱学是一种增强的“看”模式，人们根据光子的能量或波长来分离光子。这个项目的核心是使用光谱学来探索、阐明和理解受相关性、挫折和复杂性影响的材料的基本性质和应用潜力。钨酸锆的纳米尺度结构包括惊人的大开阔空间和原子自由感，这种自由感被称为“欠约束”。钨酸锆在受热时也会收缩，这一现象被称为负热膨胀。光谱测量将被用来阐明这种复杂化合物的异常微观结构与负热膨胀宏观现象之间的关系。这将集中在远红外声子的研究上。氧化钴钠类似于铜酸盐高温超导体，因为它有二维导电片，但不同的是，这些片中的原子结构是基于三角形而不是正方形。由于三角形晶格的“受挫”性质，由此产生的高频霍尔响应的差异，即电子在垂直于薄片的磁场存在时的反应，已被预测为显著的。该项目将寻求衡量这一影响。电子通常相互排斥，然而，在Tl掺杂和In掺杂PbTe的背景下，人们认为它们可能会相互吸引。这种不寻常的掺杂半导体的电阻，包括超导电性的意外变化，被归因于这种“负U散射”机制。这个项目将使用红外反射率测量，探索和阐明这些奇异材料中电子相互作用和传输的基本性质。这一多方面的项目集研究、教育和推广于一体。学生将准备好在现代材料的复杂和不断变化的世界中工作，这些材料与其基本和应用方面都相关。学生们还将通过我们在4年级、5年级和6年级课堂上的持续推广工作，向广大观众传达他们工作的重要性和兴奋感。技术：这一个人研究人员奖支持对材料的光谱研究，在这些材料中，相关性效应、结构复杂性和/或挫折感影响宏观现象。对钨酸锆及其相关材料的远红外反射率的研究将考察结构欠约束、异常声子现象和负热膨胀之间的关系，以及这些复杂材料中可能的冰状行为和几何挫折的表现。测量层状钴氧化物的有限频率霍尔响应将在三角形晶格的背景下研究强关联的影响，对于三角形晶格，三边磁通封闭环可能主导响应。对Tl和In掺杂PbTe的光学和远红外反射率的研究将试图阐明在这些系统中观察到的新的输运现象的起源，其中反常的掺杂特性和输运与负U散射有关。这个多方面的项目集研究、教育和实践于一体。学生将准备在与基础和应用方面相关的现代材料的复杂和不断变化的世界中工作，并向广大受众传达他们工作的重要性和兴奋感。

Non-Technical:Spectroscopy is an enhanced mode of "seeing" in which one separates photons according to their energy or wavelength. This project centers on the use of spectroscopy to explore, elucidateand understand the fundamental nature and application potential of materials influenced by correlation, frustration and complexity. The nanoscale structure of zirconium tungstate includes surprisingly large open spaces and a sense of atomic freedom know as "underconstraint".Zirconium tungstate also contracts when it is heated, a phenomenon known as negative thermal expansion. Spectroscopic measurements will be utilized to elucidate the relationship between the unusual microscopic structure of this complex compound and the macroscopic phenomenon of negative thermal expansion. This will center on the study of far-infrared phonons. Sodium-cobalt-oxide is similar to cuprate high-temperature superconductors in that it has two-dimensional conducting sheets, however, it is different in that the atomic structure within these sheets is based on triangles rather than squares. The resulting difference in the high-frequency Hall response, i.e., the reaction of electrons in the presence of a magnetic field perpendicular to the sheets, has been predicted to be significant due to the "frustrated" nature of the triangular lattice. This project will seek to measure this effect. Electrons normally repel each other, however, in the context of Tl-doped and In-doped PbTe it has been suggested that they may attract one another.Unexpected changes in the electrical resistance of this unusual doped semiconductor, including superconductivity, have been attributed to such a "negative-U scattering" mechanism. This project will use infrared reflectivity measurements explore and elucidate the fundamental nature of the electron interactions and transport in these exotic materials. This multifaceted project integrates research, education and outreach. Students will be prepared to work in the complex and changing world of modern materials relevant for both their fundamental and applied aspects. Students will also be taught to communicate the importance and excitement of their work to broad audiences through our ongoing outreach efforts in4th, 5th and 6th grade classrooms.Technical:This individual investigator award supports spectroscopic studies of materials in which correlation effects, structural complexity and/or frustration influence macroscopic phenomena. Studies of far-infrared reflectivity in zirconium tungstate and related materials will examine relationships between structural underconstraint, unusual phonon phenomena and negative thermal expansion, as well as possible ice-like behavior and manifestations of geometrical frustration in these complex materials. Measurements of finite-frequency Hall response in layered cobalt oxides will investigate the influence of strong correlations in the context of a triangular lattice for which 3-sided flux-enclosing loops may dominate the response. Studies of the optical and far-infrared reflectivity of Tl- and In-doped PbTe will seek to elucidate the origins of novel transport phenomena observed in these systems where anomalous doping characteristics and transport have been associated with negative-U scattering. This multifaceted project integrates research, education and outreach.Students will be prepared to work in the complex and changing world of modern materials relevant for both fundamental and applied aspects, and to communicate the importance and excitement of their work to broad audiences.