Moment Localization and Delocalization in f-Electron Compounds

f 电子化合物中的矩局域化和离域化

• 批准号: 0907457
• 负责人: Meigan Aronson
• 金额: $ 37.5万
• 依托单位: SUNY at Stony Brook
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2009
• 资助国家: 美国
• 起止时间: 2009-08-15 至 2013-07-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0907457&HistoricalAwards=false
• 关键词: Moment; Localization; Delocalization; Electron; Compounds; Moment; Localization; Delocalization; Electron; Compounds

Technical AbstractThe fundamental properties of correlated electron materials such as their ability to conduct heat or electricity, whether they sustain static and localized moments or charges, and indeed how these complex systems approach their ultimate ground states reflect the degree to which their electrons are localized or delocalized. In f-electron systems, most notably heavy electron compounds, electrons initially localized on f-orbitals can be delocalized, expanding the Fermi surface. Of special interest is when this localization - delocalization occurs at a T=0 quantum critical point, which separates a magnetically ordered state where the electron is localized and does not participate in the Fermi surface, from a paramagnetic and strongly interacting metal where the f-electron is fully incorporated in the Fermi surface. This project will track this moment deconfinement transition away from the quantum critical point to higher temperatures and investigate its relationship to Kondo coherence, where f-electrons are thought to delocalize by the hybridization of individually Kondo compensated moments. The project will pursue this program in the YbTX compounds, where with an appropriate choice of transition metal T and main group element X we can span all regimes of the heavy electron phase diagram. It has also been suggested that strong quantum fluctuations associated with geometrical frustration may separate magnetic localization from the quantum critical point. This possibility will be investigated in the R2T2X (R=Ce,Yb) Shastry-Sutherland compounds. This program will combine the synthesis of new f-electron compounds, and their investigation using neutron scattering experiments as well as lab-based magnetometry, specific heat, and electrical transport measurements. The project makes extensive use of national research facilities, and the students trained will be well prepared to become effective future users. By learning a variety of different synthesis and characterization techniques, participating students will develop a valuable and very portable set of skills, and through the excitement of performing the first measurements on materials of their own invention, will gain the motivation to sustain them in their future careers as materials-inspired scientists. Non-Technical AbstractJust as changing temperature can cause water to fundamentally change its properties from solid to liquid to vapor; other properties of materials can similarly be transformed by varying temperature, pressure, or magnetic field: metal to insulator, magnet to non-magnet, conductor to superconductor. The ability to control these phase transitions is central to implementing new generations of sensors, where for instance small magnetic fields transform a conductor into a nonconductor, or a small change in temperature can cause a magnet to become nonmagnetic. These effects become strongest when the phase transitions occur at the lowest temperatures, and it is the purpose of this research to study the most extreme of magnetic phase transitions, where magnetism is stable only at zero temperature. The goal of this research is to understand the underlying factors which control the stability of magnetism, information which will be used to design new generations of magnetic materials with improved functionality for applications as diverse as magnetic data storage and energy control. This project will develop new families of materials to enable this research, where the strength of the magnetism and its onset temperature will be varied compositionally. We will document the corresponding changes in the material's ability to conduct heat and electricity, and the strength of the magnetism induced in the material as we drive it ever closer to the composition where magnetism is no longer possible. Very near this magnetic instability itself, the magnetism exists only ephemerally, and over only short length scales. Neutrons can be used to microscopically probe these magnetic fluctuations. Scattering experiments will be performed at national neutron scattering facilities such as those at NIST in Gaithersburg MD and the Spallation Neutron Source in Oak Ridge TN. It is increasingly recognized that the dearth of scientists trained in synthesis techniques is placing US competitiveness in materials inspired research at risk. The project focus is to synthesize new materials with very specific functionality. Participating undergraduate and graduate students will learn a variety of different synthesis techniques, as well as the arsenal of experimental techniques required to certify the high quality of the samples. Students participating in this program develop a highly sought and very portable skill set, which has already proven of great value to themselves and their future employers.

技术摘要，相关电子材料的基本特性，例如它们进行热或电力的能力，无论它们是否维持静态和局部矩或电荷，实际上这些复杂系统如何接近它们的最终基础状态，反映了其电子的局部或分离。 在F-电子系统中，最著名的是重型电子化合物，最初位于F-轨道上的电子可以被驱逐到轨道上，从而扩展了费米表面。 特别感兴趣的是，当这种定位 - 定位发生在t = 0量子临界点上时，将电子局部定位并且不参与费米表面的磁性状态与副磁性和强烈相互作用的金属，其中F -Electron完全掺入Fermi表面中。 该项目将跟踪这一刻从量子临界点到较高温度的转换过渡，并调查其与昆多连贯性的关系，在这种情况下，人们认为F-电子通过杂交的杂交量造成的补偿力矩的杂交被认为可以降落。 该项目将在YBTX化合物中追求该程序，其中适当选择过渡金属T和主要组元素X可以跨越重电子相图的所有制度。还有人提出，与几何挫败感相关的强量子波动可能会将磁定位与量子临界点分开。 这种可能性将在R2T2X（r = CE，YB）的Shastry-Sutherland化合物中进行研究。 该程序将结合新的F-电子化合物的合成，并使用中子散射实验以及基于实验室的磁力测定法，比热和电运输测量结果进行研究。该项目广泛利用国家研究设施，受过培训的学生将做好充分的准备，以成为有效的未来用户。通过学习各种不同的综合和表征技术，参与的学生将发展一套有价值且非常便携的技能，并通过对自己发明的材料进行首次测量的兴奋，将获得动力，以将他们作为材料启发的科学家作为材料启发的未来职业维持。非技术抽象作为变化的温度会导致水从根本上将其特性从固体变为液体变为蒸气。材料的其他特性可以通过不同的温度，压力或磁场来转换：金属到绝缘体，磁铁到非磁铁，导体，超导体。 控制这些相变的能力对于实现新一代传感器至关重要，例如，小磁场将导体转化为非导体，或者温度的较小变化可能导致磁体变得非磁性。 当相变发生在最低温度下时，这些效果变得最强大，这是研究最极端的磁相跃迁的目的，其中磁性仅在零温度下稳定。 这项研究的目的是了解控制磁性稳定性的潜在因素，这些信息将用于设计具有改进功能的新一代磁性材料，以适应磁性数据存储和能量控制等多样化的应用。 该项目将开发新的材料家族来实现这项研究，在该研究中，磁性的强度及其发作温度将在构图上变化。 我们将记录材料传导和电力能力的相应变化，以及材料中引起的磁性强度，因为我们将其越来越接近不再可能磁性的组成。磁性本身很近，磁性仅在短长度上存在，并且仅在短长度上存在。 中子可用于微观探测这些磁波动。散射实验将在全国性中子散射设施中进行，例如医学博士NIST的NIST和Oak Ridge TN中的散布中子源。 人们越来越认识到，接受合成技术培训的科学家的缺乏使美国在材料中的竞争力启发了风险的研究。该项目的重点是综合具有非常具体功能的新材料。 参与的本科生和研究生将学习各种不同的合成技术，以及证明样品高质量所需的实验技术的武器库。 参加该计划的学生开发了一种备受追捧且非常便携的技能，这已经证明对自己和未来的雇主具有巨大的价值。