Noise Investigations of Condensed Matter Systems

凝聚态系统的噪声研究

• 批准号: 9623478
• 负责人: Michael Weissman
• 金额: $ 24.35万
• 依托单位: University of Illinois at Urbana-Champaign
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 1996
• 资助国家: 美国
• 起止时间: 1996-09-01 至 2000-02-29
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=9623478&HistoricalAwards=false
• 关键词: Noise; Investigations; Condensed; Matter; Systems

w:\awards\awards96\*.doc 9623478 Weissman Non-Gaussian noise statistics will be used to probe statics and dynamics of some important problems in disordered condensed matter. Six central topics are identified. The first project will address the pinning of magnetic flux by disorder in some of the new superconducting materials. This includes a study of the process by which the flux breaks loose, destroying superconductivity, at high currents.The second project will investigate the role of inhomogeneous conductance among small magnetic regions in determining the mechanism for colossal magnetoresistance. The third topic will study the effect on the "solidity" of the glass phase of some hidden long-range order, such as large-scale collective rearrangements well below the temperature at which gross annealing sets in. The forth topic consists in the study of the effect of local anisotropy in determining the qualitatively different mesoscopic behavior of different metallic spin-glasses. The fifth project will study which of the two mechanisms, simple pinning of magnetic domain walls or collective domain-wall rearrangements, is the most important in determining the unevenness of the magnetization process in most magnets. The nature of relaxor ferroelectric behavior and comparison to spin-glass-like phenomenon will be the last issue to be studied. %%% Almost all real materials are not perfectly crystalline, but rather have some disorder. In many cases (e.g. glasses), this disorder is fundamental to the structural properties of the material, in other cases (e.g. superconductors in a magnetic field) it is crucial to understanding the dynamical behavior. Generally, disorder creates situations in which there are multiple states among which the system can switch, either by thermal energy or under the influ ence of external driving. Such switches create noise in measurable properties. The goal of this project is to clarify how certain disordered structures form and respond to external driving, mostly by using noise as a probe. The central issues to be addressed are: (1) In glasses, is some hidden long-range order responsible for the "solidity" of the glass phase, despite the apparent randomness of the structure? At what temperature do large-scale collective rearrangements occur in glasses? (2) In the magnetic relative of glasses, spin- glasses, what parameters determine the range and form of the collective behavior? In technological important relaxor ferroelectrics, what determines the same properties? (3) How does the underlying disorder in most magnets create the unevenness of the magnetization process? Is a simple pinning of magnetic domain walls involved, or are collective domain-wall rearrangements important? (4) In the colossal magnetoresistive materials, investigated as promising field sensors for magnetic recording and other applications, what is the main mechanism of the magnetoresistive effect? Is inhomogeneous conductance among small magnetic regions the key process?

w:\awards\awards96\*.doc 9623478 Weissman 非高斯噪声统计将用于探测无序凝聚态物质中一些重要问题的静力学和动力学。确定了六个中心主题。第一个项目将解决一些新型超导材料中无序引起的磁通量钉扎问题。这包括研究高电流下磁通松散、破坏超导性的过程。第二个项目将研究小磁性区域之间的不均匀电导在确定巨磁阻机制中的作用。第三个主题将研究一些隐藏的长程有序对玻璃相“坚固性”的影响，例如远低于粗退火开始温度的大规模集体重排。第四个主题包括研究局部各向异性在确定不同金属自旋玻璃的定性不同介观行为中的影响。第五个项目将研究两种机制（磁畴壁的简单钉扎或集体畴壁重排）中的哪一种对于确定大多数磁体磁化过程的不均匀性最重要。弛豫铁电行为的本质以及与类自旋玻璃现象的比较将是最后一个要研究的问题。 %%% 几乎所有真实的材料都不是完美的结晶，而是有一些无序。在许多情况下（例如玻璃），这种无序是材料结构特性的基础，而在其他情况下（例如磁场中的超导体），它对于理解动态行为至关重要。 一般来说，无序会造成系统可以通过热能或外部驱动的影响在多种状态之间切换的情况。 此类开关会在可测量的属性中产生噪声。该项目的目标是阐明某些无序结构如何形成以及如何响应外部驱动，主要通过使用噪声作为探针。 要解决的核心问题是：（1）在玻璃中，尽管结构具有明显的随机性，但是否存在某种隐藏的长程有序导致了玻璃相的“坚固性”？玻璃中发生大规模集体重排的温度是多少？ (2) 在玻璃的磁性亲戚自旋玻璃中，哪些参数决定了集体行为的范围和形式？ 在技​​术重要的弛豫铁电体中，是什么决定了相同的特性？ (3) 大多数磁体的基本无序是如何造成磁化过程不均匀的？是否涉及磁畴壁的简单钉扎，或者集体磁畴壁重新排列是否重要？ (4) 在巨大的磁阻材料中，作为磁记录和其他应用的有前景的场传感器，磁阻效应的主要机制是什么？小磁区之间的电导不均匀是关键过程吗？