Quantum Critical Behavior at Metal-Insulator and Magnetic Transitions

零温度下的相变涉及到全新的物理学。海森堡不确定性原理不可避免地将材料变化状态的静态和动态响应交织在一起，引入了新的临界指数，新的标度律，以及相互作用和无序之间的新关系。 本项目将在两个模型实验系统中探索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-绝缘体转变。 稀土氢化物薄膜可以通过简单地改变氢含量或通过紫外线曝光从金属镜可逆地转化为透明的绝缘窗。 Mott-Hubbard MI过渡在金属氢化物薄膜的物理将追求强调电子-电子相互作用，由不同类型的无序，并在电场和磁场中的（非线性）动态响应所发挥的作用。 第二个模型系统涉及单晶的唯一元素反铁磁体，铬。 用少量的钒稀释铬，将Cr的自旋密度波跃迁平稳地抑制到T = 0。 一个简单的反铁磁体是否会表现出相关的高温超导体和重费米子化合物所表现出的反常行为？实验的重点将是在超低温下的高分辨率压力研究，广泛发展本科生，博士和博士后水平的学生的技术技能。%材料通常会随着温度的变化而发生状态变化。 压力和磁场等非热过程也可以引起磁、电和光的变化。 当这些跃迁发生在绝对零度时，所有的运动都停止了，新的量子物理学就出现了。 此外，这些影响可以在令人惊讶的高温下感受到。该方案的目的是在两个模型实验系统中探索量子相变的基本性质。 其中第一个是元素Y和La的氢化膜中的金属-绝缘体转变。稀土氢化物薄膜可以可逆地从金属镜转化为透明的绝缘窗，只需改变周围的氢气压力或通过紫外光照射。 具有均匀和像素化光学特性的可切换反射镜将被研究，并考虑到应用。 第二个模型系统涉及单晶的唯一元素反铁磁体，铬。 用少量的钒（元素周期表中与铬相邻的元素）稀释铬，可以将磁转变温度平稳地降低到绝对零度。 一个简单的反铁磁体是否会表现出相关高温超导体所表现出的反常行为？ 实验重点将是在超低温下的高分辨率压力研究，广泛发展本科生，博士生和博士后水平的学生的技术技能。

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.***