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

小行星970 这是一个新的项目，由一个PI谁与一个完善的科学家小组合作，加州大学圣地亚哥分校研究“高度相关的电子系统”。 这些都是复杂的系统，超导性、磁性、金属导电性和绝缘性都存在于同一个材料系统中，通常在组成或结构上只有很小的变化。 单电子能带窄，屏蔽有限，电子-电子关联能高，导致电子系统对不同竞争基态的普遍不稳定性。 在这种不稳定性的附近，降低维数从而增加关联能或增加磁矩的效果可能是极其显著的。 这种复杂性是 在更传统的材料中不存在，在更传统的材料中，通常可以使用费米液体理论相当成功地描述性质，并且微小的变化很少导致显著的效果。 在这些复杂的系统中，测量同一样品的所有特性的重要性 不能 言过其实，因为微妙和 经常 几乎不可测量的结构或化学变化可以剧烈地影响性能。 从低温到任何相变的比热测量揭示了电子系统的重要特性。 我们能够测量薄膜和微克级单晶的比热，因此可以测量相同样品的磁输运、磁化、IR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 可以 被 变化，或者通过 组合物 或 降维，并与理论家沙姆，阿罗瓦斯，雷恩发展模型，为这些材料。 %这是一个新的项目，由PI谁与一个良好的建立科学家组合作，加州大学圣地亚哥分校研究“高度相关的电子系统”。 这些材料在凝聚态物理中引起了极大的兴趣，并具有巨大的应用潜力，如 作为 高 温度 超导体 或 巨大磁电阻。 这些材料的相图是复杂的，具有超导性、磁性、金属导电性或绝缘性，在相同的材料系统中可以找到，通常在组成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，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，根据结构或组成的极其细微的差异，它们可能走向不同的方向。 考虑到这一点，测量同一样品的所有特性的重要性再强调也不为过，因为这些特性是微妙的，通常 几乎无法测量的结构或化学 变化 会严重影响性能。 我们有一个独特的能力，在这里进行基本的测量（比热）的样品，无法测量 其他地方 这笔赠款将 允许 美国 到 利用我们独特的专业知识以及其他公司在样品制备、表征、测量和理论理解方面的专业知识，开展合作。 ***

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. ***