The Microscopic Electronic Structure of Iron Superconductors Under Strain: New Frontiers in Scanning Probe Microscopy

应变下铁超导体的微观电子结构：扫描探针显微镜的新领域

• 批准号: 1610110
• 负责人: Abhay Pasupathy
• 金额: $ 42万
• 依托单位: Columbia University
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2016
• 资助国家: 美国
• 起止时间: 2016-09-01 至 2020-08-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1610110&HistoricalAwards=false
• 关键词: Microscopic; Electronic; Structure; Iron; Superconductors

Non-technical Abstract:When a material is mechanically stretched, its properties can undergo dramatic changes. For example, we are familiar with how the elasticity of rubber changes as it is stretched. Less familiar but equally important are changes to the electronic properties of materials. When stretched, materials can change their electrical resistance, light absorption and a host of other electronic properties. The causes for such changes in the electronic properties are often poorly understood at the microscopic level. In this project, the research team will use scanning tunneling microscopy (STM) to study the electronic properties of materials as they are stretched. STM is a technique to measure the electronic properties of materials with the precision of single atoms. In this research, a specially designed apparatus is used to mount and stretch crystal materials in the STM while their response is monitored. This equipment is designed, manufactured, assembled and run by the principal investigator's research team. It is used to impart training to students at the high school, undergraduate and graduate levels, and is used to liaison with industrial partners. The goal of the project will be to develop a microscopic understanding of the changes brought about by strain in materials, especially those belonging to the iron pnictide class of superconductors. Technical abstract:External strain when applied to materials can cause electronic changes via modifying band structure, interaction strengths and even changes in phase. Understanding the microscopic changes brought about by the application of strain is the key scientific problem of interest in this project. The main scope of the research is to study the electronic nematic phase of the iron pnictides. In this phase, electronic properties display nematicity, the spontaneous breaking of the underlying discrete rotational symmetry of the lattice. Developing an understanding of the nematic electronic phase and its coupling to the other phases of these materials is the key scientific goal of this project. The main experimental technique used will be atomic-resolution, cryogenic STM measurements. The project is enabled by a technical breakthrough that allows for the very first time the application of uniaxial or biaxial in-plane strains to a sample, while continuously performing microscopic measurements on the same atomically resolved area of the surface. Using this apparatus, STM is used to measure (a) gaps from spectroscopy (b) domain structure from topography and (c) scattering rates from quasiparticle interference, all under the influence of strain. The apparatus is used across the phase diagram in three different pnictide families of NaFe(Co)As, Fe(Te)Se and LiFe(Co)As systems that display very different nematic behaviors. The final goal of the project is to determine the driving forces for nematicity and its connection to superconductivity in the pnictides.

摘要：当材料受到机械拉伸时，其性能会发生巨大变化。例如，我们熟悉橡胶的弹性是如何随着拉伸而变化的。人们不太熟悉但同样重要的是材料电子特性的变化。当拉伸时，材料可以改变其电阻、光吸收和许多其他电子特性。这种电子性质变化的原因在微观层面上往往很难理解。在这个项目中，研究小组将使用扫描隧道显微镜（STM）来研究材料拉伸时的电子特性。STM是一种以单原子精度测量材料电子特性的技术。在这项研究中，一个特殊设计的装置被用来安装和拉伸晶体材料在STM中，同时监测它们的响应。该设备由首席研究员的研究团队设计、制造、组装和运行。它用于向高中、本科和研究生阶段的学生传授培训，并用于与工业合作伙伴联络。该项目的目标将是对材料中应变带来的变化进行微观理解，特别是那些属于铁镍类超导体的材料。技术摘要：外部应变作用于材料时，可以通过改变能带结构、相互作用强度甚至相位变化引起电子变化。了解应变的应用所带来的微观变化是本项目感兴趣的关键科学问题。本研究的主要范围是对铁类化合物的电子向列相进行研究。在这一阶段，电子性质表现为向列性，即晶格离散旋转对称性的自发破缺。发展对向列电子相及其与这些材料的其他相的耦合的理解是这个项目的关键科学目标。使用的主要实验技术将是原子分辨率，低温STM测量。该项目是由一项技术突破实现的，该技术首次允许对样品进行单轴或双轴平面内应变，同时在相同的表面原子分辨区域连续进行微观测量。利用该仪器，STM用于测量(a)光谱的间隙(b)形貌的畴结构和(c)准粒子干涉的散射率，所有这些都在应变的影响下。该仪器在三种不同的相图中使用：NaFe(Co)As, Fe(Te)Se和LiFe(Co)As体系，它们表现出非常不同的向列行为。该项目的最终目标是确定向列性的驱动力及其与粒子中超导性的联系。