Electron Spectroscopy Studies of Quantum Emergence in Low Dimensional Systems

*非技术摘要*材料的电、磁和机械性能是？紧急集体行为？它们的电子和组成原子的基本量子力学。固体物理学和材料科学的一个主要目标就是解释这种现象。这一目标的完全实现将意味着有能力设计出对任何特定应用都是最佳的材料。目前对固体中电子的主要理解是一套被称为“费米液体理论”的深刻观点。这一理论解释了为什么固体中的电子通常可以用一幅简单的图画来描述，这幅图似乎忽略了已知的电子相互作用的巨大排斥力。越来越多的人认识到，这一理论可能不适用于整个类别的可能有用的材料，有人怀疑，这种失败与不同可能出现的行为之间尚未解决的竞争有关。这项研究拨款支持一项实验计划，该计划旨在使用一种名为电子光谱学的技术来测量和量化材料中电子的潜在量子力学行为，这些材料表现出这种未解决的竞争，因为它们的晶体结构是准一维或准二维的。如果成功，这项工作将确定基本的想法，这些想法必须结合在一起，将工程材料的目标带到下一个复杂的水平。这些实验既在密歇根大学的家庭实验室进行，也在各种国家和国际同步加速器设施中进行。该计划依赖于与世界各地其他组织的密切合作，以提供表征良好的样品进行测量，确定新材料的电、热和磁性能，并提供专家理论建议和高级计算。因此，它建立了跨越地理、机构和学科边界的人与人之间的桥梁。它还使项目人员，包括学生，与在不同机构担任各种专业角色的科学家密切接触，并培训他们合作工作的技术。从而为我国S人文科学资源做出贡献。还鼓励项目人员寻找机会，在公共讲座或科学咖啡馆等场所向公众解释他们的工作。*强相关的电子材料通过它们表现出的惊人的量子基态范围来表现出紧急现象，例如，绝缘的、金属的、磁性的、超导的，化学成分、温度或压力明显微不足道或轻微变化。最近人们非常感兴趣的是处于两个稳定的零温度基态之间的系统的行为，即在一个量子临界点。这些行为本质上支持非费米液体(NFL)现象，包括一维相互作用电子气中以受阻有序为特征的电子分馏。这项研究计划使用光电子能谱和逆光电子能谱技术来测量选定的低维材料的单粒子电子结构，并试图识别出现的量子结构及其与底层电子结构的关系。如果完全成功，这项工作可能会为以下问题提供一个尖锐的答案：在与纯粹一维理论模型相关的性质的一个维度以上，是否存在与稳定化相关的新的物质量子态。这些实验既在密歇根大学的家庭实验室进行，也在各种国家和国际同步加速器设施中进行。实验数据通过与以不同方式处理库仑相互作用的理论进行比较来分析，这些理论提供了光谱与电或磁性质之间的联系。该计划依赖于与世界各地其他组织的密切合作，以提供表征良好的样品进行测量，确定新材料的电、热和磁性能，并提供专家理论建议和高级计算。因此，它建立了跨越地理、机构和学科边界的人与人之间的桥梁。它还使项目人员，包括学生，与在不同机构担任各种专业角色的科学家密切接触，并培训他们合作工作的技术。项目人员也被鼓励寻找机会在公开讲座或科学咖啡馆-S-向公众解释他们的工作。

*****NON-TECHNICAL ABSTRACT****Electrical, magnetic and mechanical properties of materials are ?emergent collective behaviors? of the underlying quantum mechanics of their electrons and constituent atoms. A principal goal of solid state physics and materials science is to elucidate this emergence. A full achievement of this goal would imply the ability to engineer a material that is optimum for any particular application. The mainstay of the current understanding of electrons in solids is a set of deep ideas known as the "Fermi liquid theory." This theory explains why electrons in solids can often be described in a simplified picture which appears to ignore the large repulsive forces that electrons are known to exert on one another. There is a growing appreciation that this theory probably fails for entire classes of possibly useful materials and there is the suspicion that the failure has to do with unresolved competition between different possible emergent behaviors. This research grant supports an experimental program aimed at using a technique called electron spectroscopy to measure and quantify the underlying quantum mechanical behaviors of electrons in materials which manifest this unresolved competition because their crystal structures are quasi-one or quasi-two dimensional. If successful the work will pinpoint essential ideas that must be combined to take the goal of engineering materials to the next level of sophistication. The experiments are performed both in a home laboratory at the University of Michigan, and at various national and international synchrotron facilities. The program relies on strong collaborations with other groups around the world for the providing of well characterized samples to measure, for determining electrical, thermal and magnetic properties of new materials, and for expert theoretical advice and advanced calculations. It thus builds human bridges across geographic, institutional and disciplinary boundaries. It also brings program personnel, including students, into close contact with scientists in a variety of professional roles at a variety of institutions, and trains them in the techniques of collaborative work. Thereby it contributes to our country?s human scientific resources. Program personnel are also encouraged to seek opportunities to explain their work to the public in settings such as public lectures or science cafes. *****TECHNICAL ABSTRACT****Strongly correlated electron materials manifest emergent phenomena by the remarkable range of quantum ground states that they display, e.g., insulating, metallic, magnetic, superconducting, with apparently trivial, or modest changes in chemical composition, temperature or pressure. Of great recent interest are the behaviors of a system poised between two stable zero temperature ground states, i.e. at a quantum critical point. These behaviors intrinsically support non-Fermi liquid (NFL) phenomena, including the electron fractionalization that is characteristic of thwarted ordering in a one-dimensional interacting electron gas. This research program uses the techniques of photoemission and inverse photoemission spectroscopies to measure the single-particle electronic structures of selected low dimensional materials and seeks to identify emergent quantum structures and their relation to the underlying electronic structure. If fully successful, the work could provide a sharp answer to the question of whether or not there are new quantum states of matter associated with the stabilization in higher than one dimension of properties associated with purely one dimensional theory models. The experiments are performed both in a home laboratory at the University of Michigan, and at various national and international synchrotron facilities. The experimental data are analyzed by comparison to theories which treat the Coulomb interactions in different ways, and which provide a link between the spectra and the electrical or magnetic properties. The program relies on strong collaborations with other groups around the world for the providing of well characterized samples to measure, for determining electrical, thermal and magnetic properties of new materials, and for expert theoretical advice and advanced calculations. It thus builds human bridges across geographic, institutional and disciplinary boundaries. It also brings program personnel, including students, into close contact with scientists in a variety of professional roles at a variety of institutions and trains them in the techniques of collaborative work. Program personnel are also encouraged to seek opportunities to explain their work to the public in settings such as public lectures or science cafe?s.