Electron Correlations at the Edge of Instability: Complex Materials and Restricted Geometries

不稳定边缘的电子相关性：复杂材料和受限几何形状

• 批准号: 9705300
• 负责人: Frances Hellman
• 金额: $ 41.5万
• 依托单位: University of California-San Diego
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 1997
• 资助国家: 美国
• 起止时间: 1997-09-01 至 2002-08-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=9705300&HistoricalAwards=false
• 关键词: Electron; Correlations; Edge; Instability; Complex

9705300 Hellman This is a new project by a PI who collaborates with a well established group of scientists a UC San Diego to study "highly correlated electron systems". These are complex systems, with superconductivity, magnetism, metallic conduction, and insulating behavior found in the same material system, often with only small changes in composition or structure. One electron bands are narrow, screening is limited, and electron-electron correlation energy is high, leading to a general instability of the electronic system to different competing ground states. In the neighborhood of such instabilities, the effects of reducing dimensionality, thereby increasing the correlation energy, or of adding magnetic moments can be extremely dramatic. This complexity is absent in more traditional materials, where properties can generally be quite successfully described using Fermi liquid theory, and dramatic effects seldom result from small changes. In these complex systems the importance of measuring all properties on the same sample cannot be overstated, since subtle and often nearly unmeasurable structural or chemical changes can drastically affect properties. Measurements of specific heat from low temperature up through any phase transitions reveal important characteristics of the electronic system. Our ability to measure the specific heat of thin films and microgram size single crystals allows measurements of magneto-transport, magnetization, IR and tunneling spectroscopy on the same samples. We plan collaborations with Maple, Schuller, Basov, and Dynes to prepare and measure samples of materials in which correlation energies can be varied, either by composition or reduced dimensionality, and with theorists Sham, Arovas, and Renn to develop models for these materials. %%% This is a new project by a PI who collaborates with a well established group of scientists a UC Sa n Diego to study "highly correlated electron systems". These are materials causing great excitement in condensed matter physics and with great potential for applications, such as high temperature superconductors or colossal magnetoresistance. The phase diagrams of these materials are complex, with superconductivity, magnetism, metallic conduction, or insulating behavior found in the same material system, often with only small changes in composition or structure. This complexity is absent in more traditional materials. The interactions between the electrons, which cause the magnetism, superconductivity, or insulating behavior, compete with each other, with one or another winning. It thus appears that the electrons in these new materials are perched on the edge of many different types of behavior, with the potential to go different ways depending on extremely subtle differences in structure or composition. With this in mind, the importance of measuring all properties on the same sample cannot be overstated, since subtle and often nearly unmeasurable structural or chemical changes can drastically affect properties. We have a unique capability here to make a basic measurement (specific heat) on samples which cannot be measured elsewhere. This grant will allow us to develop collaborations taking advantage of our unique expertise together with others' expertise in sample preparation, characterization, measurement and theoretical understanding. ***

9705300 Hellman这是PI的一个新项目，他与一群成熟的科学家组合合作，研究了圣地亚哥分校，研究“高度相关的电子系统”。 这些是复杂的系统，具有超导性，磁性，金属传导以及在同一材料系统中发现的绝缘行为，通常只有小的组成或结构变化。 一个电子带是狭窄的，筛选有限，电子 - 电子相关能量很高，从而导致电子系统普遍不稳定不同的竞争基态。 在这种不稳定性的邻里，降低维度，从而增加相关能量或增加磁矩的影响可能是极其戏剧性的。 在更传统的材料中，这种复杂性不存在，在这种材料中，通常可以使用费米液体理论来成功地描述特性，而很少发生巨大变化，因此很少产生巨大的效果。 在这些复杂的系统中，测量同一样品上所有特性的重要性不能被夸大，因为微妙且通常几乎无法衡量的结构或化学变化会对特性产生巨大影响。 通过任何相变的低温测量特异性热量揭示了电子系统的重要特征。 我们测量薄膜和微克大小的单晶的特异性热量的能力可以测量相同样品上的磁通，磁化，IR和隧道光谱。 我们计划与Maple，Schuller，Basov和Dynes的合作，以准备和测量材料样本，其中相关能量可以通过组成或降低维度来改变相关能量，以及与理论家Sham，Arovas和Renn一起开发这些材料模型的材料。 %%％这是PI的一个新项目，他与一群成熟的科学家组合合作，一组迭戈，研究“高度相关的电子系统”。 这些材料引起了凝结物理学的极大兴奋，并且具有巨大的应用潜力，例如高温超导体或巨大的磁性。 这些材料的相图是复杂的，具有超导性，磁性，金属传导或在同一材料系统中发现的绝缘行为，通常只有小的组成或结构变化。 在更传统的材料中，这种复杂性不存在。 电子之间的相互作用，引起磁性，超导性或绝缘行为，彼此竞争，一个或另一个胜利。 因此，看来这些新材料中的电子栖息在许多不同类型的行为的边缘，并且有可能取决于结构或组成的极微妙的差异。 考虑到这一点，测量同一样品上所有特性的重要性不能被夸大，因为微妙且通常几乎无法测量的结构或化学变化会严重影响特性。 我们在这里具有独特的能力，可以对其他地方无法测量的样品进行基本测量（特定热量）。 这笔赠款将使我们能够利用我们独特的专业知识以及他人在样本准备，表征，测量和理论理解方面的专业知识开发合作。 ***