Spin, Charge, and Disorder in Correlated Metals

金属-绝缘体转变的物理性质与高度相关金属的不寻常的基态性质密切相关，包括重费米子化合物、高tc超导体和Mott-Hubbard系统V2O3和Ni(S,Se)2。一个重要的，尚未解决的问题是流动磁性与库仑相互作用和无序的相互作用的性质。本课题主要研究过渡金属氧化物和硫化物。它旨在通过电输运、磁化率、比热、中子散射和光学测量来解绕几乎离域的无序金属中自旋和电荷自由度的影响。低至毫开尔文的温度能力提供了定位和电子相互作用效应的新诊断，并简化了问题的理论描述。此外，通过对输运和量热响应的高分辨率压力研究，应该揭示出与通常费米-液体行为的可能偏差，以及量子和经典状态下假设的不同形式。从电子可以自由流动的状态到电子不能移动的状态的急剧变化是许多设备应用的核心。这种“金属-绝缘体”的转变可以由许多外部参数驱动，包括压力的应用、无序的引入和材料特性的操纵。这里提出的研究旨在探索在所有真实材料中发现的无序和控制参数之间的相互作用，例如改变电子密度和金属与绝缘体之间边界的内部化学压力。主要关注的是过渡金属氧化物和硫化物，这类材料的电子和磁性响应对控制参数的微小变化非常敏感。根据特定的材料及其制备的性质，它可能有潜力作为电子开关，磁性存储装置或高温超导体。* * *

9507873 Rosenbaum The physics of the metal-insulator transition is intimately tied to the unusual ground state properties of highly-correlated metals, including the heavy fermions compounds, the high-Tc superconductors, and the Mott-Hubbard systems V2O3 and Ni(S,Se)2. An important, unresolved issue is the nature of the interplay of the itinerant magnetism with the Coulomb interactions and the disorder. This research project focuses on the transition metal oxides and sulfides. It aims to deconvolute the influences of the spin and charge degrees of freedom in the barely-delocalized, disordered metal through a program of electrical transport, magnetic susceptibility, specific heat, neutron scattering, and optical measurements. Temperature capabilities down to the milliKelvin regime provide new diagnostics of localization and electron interaction effects as well as simplifying the theoretical description of the problem. Moreover, possible deviations from the usual Fermi-liquid behavior, with different forms posited for the quantum and classical regimes, should be revealed by high-resolution pressure studies of the transport and calorimetric response. %%% A sharp change from a state where electrons can flow freely to one where they are unable to move lies at the heart of many device applications. This "metal-Insulator" transition can be driven by a number of external parameters, including the application of pressure, the introduction of disorder, and the manipulation of material characteristics. The research proposed here seeks to explore the interaction between disorder, found in all real materials, and control parameters such as changing electron density and internal chemical pressure at the boundary between metal and insulator. Of prime interest are transition metal oxides and sulfides, classes of materials whose electronic and magnetic responses are acutely sen sitive to small changes in the control parameters. Depending on the particular material and the nature of its preparation, it may have potential as an electronic switch, a magnetic storage device, or a high- temperature superconductor. ***