Quantum Critical Behavior at Metal-Insulator and Magnetic Transitions

金属-绝缘体和磁转变的量子临界行为

• 批准号: 0114798
• 负责人: Thomas Rosenbaum
• 金额: $ 33万
• 依托单位: University of Chicago
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2001
• 资助国家: 美国
• 起止时间: 2001-08-01 至 2005-07-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0114798&HistoricalAwards=false
• 关键词: Quantum; Critical; Behavior; Metal; Insulator

Phase transitions at zero temperature involve fundamentally new physics. The Heisenberg uncertainty principle inextricably intertwines the static and dynamical response of the material changing state, introducing new critical exponents, new scaling laws, and a new relationship between interactions and disorder. This project will probe the fundamental nature of the quantum phase transition in two model experimental systems. The first is the metal-insulator transition in hydrogenated films of elemental Y and La. Rare earth hydride films can be converted reversibly from metallic mirrors to transparent, insulating windows simply by changing the hydrogen content or via UV exposure. The physics of the Mott-Hubbard MI transition in metal hydride films will be pursued with an emphasis on the roles played by electron-electron interactions, by different types of disorder, and by the (non-linear) dynamical response in electric and magnetic fields. The second model system involves single crystals of the only elemental antiferromagnet, Cr. Dilution of chromium with small amounts of vanadium, smoothly depresses Cr's spin-density-wave transition to T = 0. Will a simple antiferromagnet display the anomalous behavior demonstrated by the related high-Tc superconductors and heavy fermion compounds? The experimental focus will be on high resolution pressure studies at ultra-low temperatures, broadly developing the technical skills of students at the undergraduate, doctoral and postdoctoral levels. %%%Materials most commonly undergo changes of state with changing temperature. Non-thermal processes like pressure and magnetic field also can induce magnetic, electronic, and optical changes. When these transitions occur at absolute zero, where all motion stops, new quantum physics arises. Moreover, the effects can be felt up to surprisingly high temperatures. This proposal aims to probe the fundamental nature of the quantum phase transition in two model experimental systems. The first of these is the metal-insulator transition in hydrogenated films of elemental Y and La. Rare earth hydride films can be converted reversibly from metallic mirrors to transparent, insulating windows simply by changing the surrounding hydrogen gas pressure or through illumination with ultraviolet light. Switchable mirrors with both homogeneous and pixilated optical properties will be investigated, with applications in mind. The second model system involves single crystals of the only elemental antiferromagnet, Cr. Dilution of chromium with small amounts of vanadium, its neighboring element in the Periodic Table, smoothly depresses the magnetic transition temperature to absolute zero. Will a simple antiferromagnet display the anomalous behavior demonstrated by the related high-temperature superconductors? The experimental focus will be on high resolution pressure studies at ultra-low temperatures, broadly developing the technical skills of students at the undergraduate, doctoral and postdoctoral levels.***

零温度下的相变涉及新的物理。海森伯格的不确定性原理无情地交织了物质变化状态的静态和动态响应，引入了新的关键指数，新的缩放定律以及相互作用与混乱之间的新关系。 该项目将在两个模型实验系统中探测量子相变的基本性质。 第一个是元素Y和LA的氢化膜中的金属晶体过渡。稀土氢化物膜可以从金属镜转化为透明，仅通过更改氢含量或通过紫外线暴露来绝缘窗户。 将追求金属氢化物膜中Mott-Hubbard MI转变的物理学，重点是通过电子 - 电子相互作用，不同类型的疾病以及电力和磁场中（非线性）动态响应的作用。 第二个模型系统涉及唯一的元素抗Fiferromagnet的单晶。 平滑降低Cr的旋转密度波过渡到t = 0的铬稀释。简单的抗fiferromagnet会显示相关的高-TC超导体和重型效费用化合物所证明的异常行为吗？实验重点将放在超低温度下的高分辨率压力研究上，并在本科，博士和博士后水平上广泛发展学生的技术技能。随着温度变化，最常见的是状态变化。 压力和磁场等非热过程也可以诱导磁，电子和光学变化。 当这些转变发生在所有运动停止的绝对零时，就会出现新的量子物理。 此外，可以感觉到高温令人惊讶的效果。该建议旨在探测两个模型实验系统中量子相变的基本性质。 其中的第一个是元素Y和La的氢化膜中的金属 - 绝缘体过渡。稀土氢化物膜可以从金属镜转化为透明，仅通过改变周围的氢气压力或通过紫外线照明来使窗户仅通过改变周围的氢气。 将研究具有均匀和像素化光学特性的可切换镜，并考虑到应用。 第二个模型系统涉及唯一的元素抗Fiferromagnet的单晶。 用少量的钒（其邻近元素在元素周期表中）稀释的铬稀释，使磁过渡温度平滑地降低至绝对零。 一个简单的抗铁磁铁会显示相关的高温超导体所证明的异常行为吗？ 实验重点将放在超低温度下的高分辨率压力研究上，从而广泛地发展了本科，博士和博士后水平的学生的技术技能。***