CAREER: Visualizing the Formation of the Charge Density Wave Phase at the Atomic Scale

职业：在原子尺度上可视化电荷密度波相的形成

• 批准号: 1056527
• 负责人: Abhay Pasupathy
• 金额: $ 59.5万
• 依托单位: Columbia University
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2011
• 资助国家: 美国
• 起止时间: 2011-07-01 至 2016-06-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1056527&HistoricalAwards=false
• 关键词: CAREER; Visualizing; Formation; Charge; Density

****NON-TECHNICAL ABSTRACT****A simple metal such as gold or copper can be imagined as an empty box with electrons bouncing around freely inside. In some solids, however, the electrons form waves in space with alternating regions of higher and lower charge. This state of matter is known as a "charge density wave" (CDW). In such solids, the formation of the charge density wave happens at a critical temperature, above which the electrons are once again free to move around. Why does this happen? How exactly do these waves of electrons form in space as the sample goes through the critical temperature? This project aims to answer this question by performing temperature-dependent scanning tunneling microscopy (STM) measurements of CDW materials to directly visualize the onset of charge density waves at the critical temperature. An STM is an instrument with which we can probe the electrons at the surface of a material with sub-atomic precision. These advanced instruments will be custom-built for this project, and the new STM measurements will give us vital information on how electrons with different energies behave in these materials as they go through the CDW transition. This project will support the education of undergraduate and graduate students in the advanced technologies required to perform STM experiments including electronics, computer-aided design, vacuum technology and cryogenics. This project seeks to answer questions about the collective motion of electrons in solids, one of the fundamental challenges in modern physics research.****TECHNICAL ABSTRACT****The aim of this project is to visualize the onset of the charge density wave (CDW) phase in real space using scanning tunneling microscopy (STM). In a simple second-order phase transition in a uniform system, the amplitude of the order parameter goes to zero at the phase transition temperature. When defects or other spatial inhomogeneity is present, the situation can be dramatically different.Using variable-temperature atomic resolution STM, recent experiments have shown that nanoscale CDW order can be stabilized above the bulk transition temperature in the transition metal dichalcogenides. How do these nanoscale patches of CDW transition to bulk CDW order? What is the local electronic spectrum in a nanoscale patch? What is the electronic spectroscopic difference between the CDW state and the normal state in these materials? What is the nature of scattering from defects and CDW patches above the transition temperature? During this project, state of the art, homebuilt STM instruments will be used to answer these questions. Graduate and undergraduate students will learn how to build and operate these instruments, and new designs for improved stability and cryogenic efficiency will be implemented. The nature of spatially ordered collective electronic phases is a topical question that arises in many modern materials, and the dichalcogenides present a clean material system where the onset of such a phase can be measured with atomic spatial precision and millivolt energy resolution.

****非技术抽象****一种简单的金属（例如金或铜）可以想象为一个空盒子，电子盒子在内部自由弹跳。但是，在某些固体中，电子在空间中形成波浪，具有较高和较低电荷的交替区域。这种物质被称为“电荷密度波”（CDW）。在这样的固体中，电荷密度波的形成发生在临界温度下，在高于该温度之上电子再次自由移动。为什么会发生这种情况？随着样品经过临界温度，这些电子波如何在太空中形成？该项目的目的是通过执行与CDW材料进行温度依赖性扫描隧道显微镜（STM）测量来直接可视化电荷密度波在临界温度下的发作。 STM是一种仪器，我们可以用它探测具有亚原子精度的材料表面的电子。这些高级仪器将是为该项目定制的，新的STM测量结果将为我们提供有关在CDW过渡时具有不同能量的电子在这些材料中如何行为的重要信息。该项目将支持在进行包括电子，计算机辅助设计，真空技术和低温学在内的STM实验所需的高级技术中的本科和研究生的教育。该项目试图回答有关固体中电子集体运动的问题，这是现代物理研究中的基本挑战之一。在均匀系统中简单的二阶过渡中，在相变温度下，顺序参数的幅度为零。当存在缺陷或其他空间不均匀性时，情况可能会大不相同。使用可变的原子分辨率STM，最近的实验表明，纳米级CDW阶可以稳定在过渡金属二核苷内化金属中的大量过渡温度之上。这些CDW的纳米级斑块如何过渡到散装CDW顺序？纳米级贴片中的局部电子光谱是什么？这些材料中CDW状态与正常状态之间的电子光谱差异是什么？从过渡温度上方的缺陷和CDW斑块中散射的性质是什么？在此项目期间，将使用最新技术的STM仪器来回答这些问题。研究生和本科生将学习如何构建和操作这些工具，并将实施提高稳定性和低温效率的新设计。空间有序的集体电子相的性质是一个局部问题，在许多现代材料中都会出现，而二分法生成层则是一个干净的材料系统，在该系统中，可以通过原子空间精度和千万能分辨率来测量这种相位的发作。