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 这是一个 PI 的新项目，他与加州大学圣地亚哥分校的一组成熟的科学家合作研究“高度相关的电子系统”。 这些是复杂的系统，在同一材料系统中具有超导性、磁性、金属传导性和绝缘性，通常在成分或结构上只有很小的变化。 电子能带窄，屏蔽有限，电子-电子相关能高，导致电子系统对不同竞争基态普遍不稳定。 在这种不稳定性附近，降低维数从而增加相关能量或增加磁矩的影响可能非常显着。 这种复杂性在更传统的材料中不存在，通常可以使用费米液体理论相当成功地描述其特性，并且微小的变化很少会产生显着的效果。 在这些复杂的系统中，测量同一样品的所有特性的重要性怎么强调都不为过，因为微妙且通常几乎无法测量的结构或化学变化会极大地影响特性。 从低温到任何相变的比热测量揭示了电子系统的重要特征。 我们能够测量薄膜和微克级单晶的比热，从而能够在同一样品上测量磁输运、磁化强度、红外和隧道光谱。 我们计划与 Maple、Schuller、Basov 和 Dynes 合作，准备和测量相关能量可以根据成分或降维变化而变化的材料样本，并与理论家 Sham、Arovas 和 Renn 合作开发这些材料的模型。 %%% 这是一个 PI 的新项目，他与加州大学圣地亚哥分校的一组成熟的科学家合作研究“高度相关的电子系统”。 这些材料在凝聚态物理领域引起了极大的兴趣，并且具有巨大的应用潜力，例如高温超导体或巨磁阻。 这些材料的相图很复杂，在同一材料系统中具有超导性、磁性、金属传导性或绝缘性，通常在成分或结构上只有很小的变化。 这种复杂性在更传统的材料中是不存在的。 电子之间的相互作用导致磁性、超导性或绝缘行为，它们相互竞争，一个或另一个获胜。 因此，这些新材料中的电子似乎处于许多不同类型行为的边缘，有可能根据结构或成分上极其微妙的差异而走不同的路。 考虑到这一点，测量同一样品的所有特性的重要性怎么强调都不为过，因为微妙且通常几乎无法测量的结构或化学变化会极大地影响特性。 我们拥有独特的能力，可以对其他地方无法测量的样品进行基本测量（比热）。 这笔赠款将使我们能够利用我们独特的专业知识以及其他人在样品制备、表征、测量和理论理解方面的专业知识来开展合作。 ***