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

非技术摘要：当材料被机械拉伸时，其性质会发生戏剧性的变化。例如，我们熟悉橡胶在拉伸时弹性如何变化。不太熟悉但同样重要的是材料电子性质的变化。当被拉伸时，材料可以改变它们的电阻、光吸收和许多其他电子特性。在微观层面上，人们对电子性质发生这种变化的原因往往知之甚少。在这个项目中，研究小组将使用扫描隧道显微镜（STM）来研究材料在拉伸时的电子特性。扫描隧道显微镜（STM）是一种以单个原子的精度测量材料电子性质的技术。在本研究中，一个特别设计的装置被用来安装和拉伸STM中的晶体材料，同时监测它们的响应。该设备由首席研究员的研究小组设计、制造、组装和运行。它用于向高中、本科和研究生一级的学生提供培训，并用于与工业伙伴联络。该项目的目标将是对材料应变所带来的变化进行微观理解，特别是那些属于铁磷属元素化物类超导体的材料。技术摘要：当施加到材料上时，外部应变可以通过改变能带结构，相互作用强度甚至相位变化来引起电子变化。了解应变应用所带来的微观变化是该项目感兴趣的关键科学问题。本文的主要研究内容是铁磷属化合物的电子相变。在这一阶段，电子性质显示向列性，自发打破潜在的离散旋转对称的晶格。发展对这些材料的电子相及其与其他相的耦合的理解是该项目的关键科学目标。主要的实验技术将是原子分辨率，低温STM测量。该项目通过技术突破实现，首次允许将单轴或双轴面内应变应用于样品，同时在表面的相同原子分辨区域上连续进行显微测量。使用该装置，STM用于测量（a）来自光谱的间隙（B）来自形貌的畴结构和（c）来自准粒子干涉的散射率，所有这些都在应变的影响下。该装置用于在三个不同的磷属元素化物家庭的NaFe（Co）As，Fe（Te）Se和LiFe（Co）As系统，显示非常不同的结晶行为的相图。该项目的最终目标是确定向列性的驱动力及其与pnictides超导性的联系。

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.