ARPES Studies of CMR Oxides and Related Materials

* 非技术摘要 * 巨磁阻（CMR）氧化物是一组重要的电子材料，其在施加磁场时呈现出其电阻的极端或巨大变化（因此称为巨磁阻）。 这些材料具有应用潜力-例如作为下一代磁存储设备中的传感器。 然而，这些材料中CMR和其他相关效应背后的大部分物理学尚未被理解。 该项目的目标是使用光电子能谱技术来促进对这些和相关材料的理解-爱因斯坦在他1905年的诺贝尔获奖论文中解释了其原理。 光电发射实验将使用紫外激光器和同步加速器辐射源（如加州伯克利实验室的高级光源）进行。 实验将在比以前更宽的参数范围内进行，预计将对这些材料的行为原因提供更深入的了解。 学生（包括本科生）在这个研究计划的包容性是很重要的，因为它将为他们提供有用的技能，为未来的职业生涯在学术界，国家实验室，或行业。 为本科生提供有意义的研究经验被认为是吸引有才华的学生并留住他们从事科学和工程职业的最有效方法之一。* 技术摘要 * 高分辨率角分辨光电发射（ARPES）将用于研究庞磁电阻（CMR）氧化物和其他相关材料的电子结构。 重点将放在双层锰氧化物的解理单晶上，这是进入这类材料的固有低能电子激发的最佳窗口。 实验将在掺杂和温度的宽参数范围内进行，以便访问并最终理解相图的复杂和丰富的演变。 在这个相图中，重要的效应是铁磁性、反铁磁性、倾斜磁性和顺磁性、金属、绝缘体、电荷和轨道有序和无序的演化。 电子间隙和赝间隙从这个顺序，以及从电子-声子耦合和本地化效应也是相关的。 这许多影响之间的合作和竞争是最终负责的“巨大的”系统的外部参数的微小变化的反应。 因此，我们的目标是了解详细的电子结构，磁结构和这些不同阶段的相互作用，以及了解这些阶段如何相互合作或竞争。 学生（包括本科生）在这个研究计划的包容性是很重要的，因为它将为他们提供有用的技能，为未来的职业生涯在学术界，国家实验室，或行业。 为本科生提供有意义的研究经验被认为是吸引有才华的学生并留住他们从事科学和工程职业的最有效方法之一。

****NON-TECHNICAL ABSTRACT****The colossal magnetoresistive (CMR) oxides are an important set of electronic materials, which present an extreme or colossal change in their electrical resistance upon the application of a magnetic field (hence the term colossal magnetoresistance). These materials have potential for applications - for example as sensors in next-generation magnetic storage devices. However, much of the physics behind CMR and other related effects in these materials is not yet understood. The goal of this project is to advance the understanding of these and related materials using the technique of photoemission spectroscopy - the principles of which were explained by Einstein in his Nobel-winning 1905 paper. The photoemission experiments will be performed with ultraviolet lasers and with synchrotron radiation sources such as the Advanced Light Source, Berkeley Labs, California. Experiments will be performed over a wider parameter range than has been done previously, which is expected to provide much deeper insights into the causes of the behavior of these materials. The inclusion of students (including undergraduates) in this research program is important, as it will provide them with useful skills for future careers in academia, national laboratories, or industry. Providing undergraduates with meaningful research experiences is considered one of the most effective ways to attract talented students and to retain them in careers in science and engineering. ****TECHNICAL ABSTRACT****High resolution angle resolved photoemission (ARPES) will be used to study the electronic structure of colossal magnetoresistive (CMR) oxides and other related materials. An emphasis will be placed on cleaved single crystals of the bilayer manganites, which give the best window into the intrinsic low energy electronic excitations of this general class of materials. Experiments will be performed over a wide parameter range of doping and temperature so as to access and eventually understand the complex and rich evolution of the phase diagram. Effects that are important in this phase diagram are the evolution of ferromagnetism, antiferromagnetism, canted magnetism, and paramagnetism, metals, insulators, charge and orbital order and disorder. Electronic gaps and pseudogaps from this order as well as from electron-phonon coupling and localization effects also are relevant. The cooperation and competition between these many effects is ultimately responsible for the "colossal" responses of the systems to minor changes in their external parameters. The goal therefore is to understand the detailed electronic structure, magnetic structure, and interactions in these various phases, as well as to understand how these phases cooperate or compete with each other. The inclusion of students (including undergraduates) in this research program is important, as it will provide them with useful skills for future careers in academia, national laboratories, or industry. Providing undergraduates with meaningful research experiences is considered one of the most effective ways to attract talented students and to retain them in careers in science and engineering.