Noise Investigations of Condensed Matter Systems

大多数材料在各种电、机械、磁和光学参数中表现出缓慢的波动，具有广泛的特征率分布。尽管这种波动的频谱普遍采用简单形式（1/f），但正如本项目过去的实验所证明的那样，涉及各种各样的机制。这些波动引起人们的兴趣主要有两个原因：首先，它们限制了各种传感器和设备的性能。其次，它们提供了一个有用的工具来研究材料的基本性质，特别是玻璃，它表现出部分冻结的随机结构。本提案应用波动技术来研究几种最常见形式的冻结紊乱的材料。这些包括非晶硅、电荷密度波系统、几种类型的自旋玻璃、自旋密度波磁畴、铁磁体的畴波动和新的巨磁阻材料。这项工作将特别强调一些驱动系统的混沌行为与平衡中存在的冻结随机性之间的相互作用。新技术通常需要新材料，并且越来越多地涉及到使用非常小的结构。在小型结构中，材料的电阻率等性质通常不是恒定的，而是随时间波动的。这种波动往往是限制设备小型化的最重要因素。该项目过去的实验表明，不同材料的这些波动背后存在着各种各样的机制。本提案探讨了一些技术上重要的材料，包括非晶硅和新的巨磁阻材料波动的起源。特别注意的是发展一个普遍的理解，但知之甚少的材料类型称为玻璃，它表现出部分冻结的随机结构。

Most materials exhibit slow fluctuations, with a broad distribution of characteristic rates, in a variety of electrical, mechanical, magnetic, and optical parameters. Despite the ubiquity of a simple form (1/f) for the frequency spectrum of such fluctuations, a wide variety of mechanisms are involved, as has been demonstrated in past experiments in this project. These fluctuations are of interest for two general reasons: First, they limit the performance of a variety of sensors and devices. Second, they provide a useful tool to study fundamental properties of materials, especially glasses, which exhibit partially frozen random structures. This proposal applied fluctuation techniques to investigate several materials with some of the most common forms of frozen disorder. These include amorphous silicon, charge-density wave systems, several types of spin-glasses, spin-density wave magnetic domains, domain fluctuations in ferromagnets, and the new giant-magneto-resistive materials. The work will emphasize particularly the interplay between the chaotic behavior of some driven systems and the frozen randomness present in equilibrium. %%% New technologies often require new materials and increasingly involve the use of very small structures. In small structures such properties as the electrical resistivity of materials are generally not constant, but fluctuate in time. Such fluctuations are often the most important factor in limiting the miniaturization of devices. Past experiments in this project have shown that a wide variety of mechanisms lie behind these fluctuations in different materials. This proposal explores the origins of the fluctuations in some technically important materials, including amorphous silicon and the new giant-magneto-resistive materials. Particular attention is paid to developing a general understanding of the very common but poorly understood types of materials known as glasses, which exhibit partially frozen random structures.