Noise Investigations of Condensed Matter Systems

在这个提议中，涨落技术将被用来探索无序凝聚态中的几个主题。巨磁阻（CMR）过渡表现出突出的非高斯噪声，这将被用来确定介观域的热力学性质，这通常是负责的磁阻效应。将研究各种CMR材料。介观巨磁电阻器件的设计是至关重要的影响，这些领域的属性。弛豫铁电体，具有巨大的介电系数和非线性压电性的无序材料，将被研究，以确定哪些影响是负责防止形成长程有序，从而保持有用的电性能。 老化实验和介观噪声实验应该能够确定弛豫有序形成的长度尺度，以及确定弛豫态中随机各向异性、随机矢量场和随机转变温度的作用。畴壁响应外场的不规则运动（巴克豪森噪声）这一普遍问题已经为人们所熟悉多年，但直到最近才有很好的理论方法来研究无序畴壁力和系统畴壁力之间的相互作用。将进行实验，以区分空间相关的障碍和集体效应的域壁的影响，以及测试有关的噪声的缩放特性的混乱的强度的想法。因为这样的测量是“小科学”，每个参与的学生（研究生和本科生）都有机会从事材料制备，微小电气设备的制造（使用材料研究实验室的先进设施），复杂的材料表征设施（在MRL），计算机编程，模拟电子学和低温技术。随着凝聚态物理学测量技术的改进，不仅可以从材料的平均特性（例如电阻），还可以从平均值周围的微小波动（例如电噪声）中提取有关材料的有用信息。这种噪声技术对于大量不规则有序的普通材料（例如玻璃）特别有价值，因为在这种材料中，平均属性通常无法传达关于无序的重要信息。例如，在最近开发的一类材料中，其电阻响应于磁场而改变很大的系数，平均响应掩盖了由噪声揭示的事实-材料并不以连续的方式均匀地改变其电阻率，而是由在不同场下突然切换的微小畴的集合组成。这些发现对于规划这些材料在小型计算机组件中的应用至关重要。因为在这个项目中进行的测量是“小科学”，每个学生参与（研究生和本科生）得到一个机会，在材料准备工作，微型电气设备的制造（使用先进的设备在材料研究实验室），复杂的材料表征设施（在MRL），计算机编程，模拟电子学和低温技术。来自这种背景和技能水平的学生在工业中需求量很大，特别是在磁存储设备的开发中。

In this proposal fluctuation techniques will be used to explore several topics in disordered condensed matter. Colossal magnetoresistive (CMR) transitions exhibit prominent non-Gaussian noise, which will be used to determine thermodynamic properties of the mesoscopic domains which are typically responsible for the magnetoresistive effect. A variety of CMR materials will be investigated. The design of mesoscopic CMR devices is crucially affected by these domain properties. Relaxor ferroelectrics, disordered materials with huge dielectric coefficients and non-linear piezo-electricity, will be investigated to determine what effects are responsible for preventing the formation of long-range order and hence for preserving the useful electrical properties. Aging experiments and mesoscopic noise experiments should be able to determine the length scale on which relaxor order forms, as well as determining the roles of random anisotropy, random vector fields, and random transition temperatures in the relaxor state. The general problem of irregular motion of domain walls (Barkhausen noise) in response to external fields has been familiar for many years, but only recently have there been good theoretical approaches to the interplay between disorder and systematic domain-wall forces. Experiments will be conducted to distinguish between effects of spatially correlated disorder and of collective effects in the domain walls, as well as to test ideas relating scaling properties of the noise to the strength of the disorder. Because such measurements are "small science", each student involved (both graduate and undergraduate) gets a chance to work on material preparation, fabrication of tiny electrical devices (using advanced facilities at the Materials Research Lab), sophisticated materials characterization facilities (at the MRL), computer programming, analog electronics, and cryogenic techniques.%%%As measurement techniques in condensed matter physics have improved, it has become possible to extract useful information about materials not only from their average properties (e.g. electrical resistance) but also from the small fluctuations around the average values (e.g. electrical noise). Such noise techniques are particularly valuable for the large number of common materials (e.g. glasses) which are not regularly ordered, because in such materials the average properties often fail to convey important information about the disorder. For example, in a recently developed category of materials whose resistance changes by a large factor in response to magnetic fields the average response obscures a fact revealed by the noise--that the material does not uniformly change its resistivity in a continuous fashion but rather consists of a collection of tiny domains which abruptly switch at different fields. Such findings are crucial in planning applications of these materials in small-scale computer components. Because the measurements undertaken in this project are "small science", each student involved (both graduate and undergraduate) gets a chance to work on material preparation, fabrication of tiny electrical devices (using advanced facilities at the Materials Research Lab), sophisticated materials characterization facilities (at the MRL), computer programming, analog electronics, and cryogenic techniques. Students from such backgrounds and skill levels are in high demand in industry, particularly in the development of magnetic storage devices.***