Neutron Spin Echo and MuSR Studies of Glassy Dynamics

玻璃动力学的中子自旋回波和 MuSR 研究

• 批准号: EP/F021178/2
• 负责人: Robert Cywinski
• 金额: --
• 依托单位: University of Huddersfield
• 依托单位国家: 英国
• 项目类别: Research Grant
• 财政年份: 2008
• 资助国家: 英国
• 起止时间: 2008 至 无数据
• 项目状态: 已结题
• 来源: https://gtr.ukri.org/projects?ref=EP%2FF021178%2F2
• 关键词: Neutron; Spin; Echo; MuSR; Studies

The nature of glass and the glass transition has been described by Physics Nobel Laureate Philip Anderson as one of the most interesting unsolved problems in physics. Despite the fact that the technology of glass manufacture has been known and exploited for thousands of years, relatively little is understood about how and why a liquid cools to a glassy rather than a well-ordered crystalline state. It is believed that that clues to the nature of the glass transition can be found by studying the evolution of the dynamical behaviour of the atoms as the transition is approached: whereas the transition to an ordered state is accompanied by relaxation which is exponentially dependent on time, it has been known since the work of Kohlrausch over 150 years ago that disordered and glassy systems relax non-exponentially. Although this non- (or stretched-) exponential relaxation seems to be ubiquitous, its origin remains controversial. Indeed it is still not clear whether it arises from parallel or hierarchical processes, or a combination of both.In some ways spin glasses, in which the orientation of the magnetic spins rather than their positions freeze into a random state, are relatively simple model systems with which to study glassy behaviour. Our recent neutron and muon beam measurements on a variety of spin glasses seem to indicate that a novel theory based upon probabilistic considerations may offer an appropriate model with which to describe the relaxation above the glass temperature. Moreover we have also demonstrated links between this model and recent thermodynamic theories based upon cooperative disorder , or non-extensive entropy, which are also useful in characterising phenomena such as earthquakes and tornadoes. If this connection can be proven we will have a scheme by which various types of both spin and structural glasses (eg fragile and strong glasses) can be understood, characterised and parameterised in terms of their fundamental thermodynamic properties. The aim of this proposal is therefore to use neutron spin echo and muon spin relaxation techniques to extend our preliminary, limited, survey of spin glasses to test rigorously the applicability of the new probabilistic relaxation theory and its relationship to the theory of non-extensive entropy in order to establish a universal thermodynamic approach to understanding the glass transition and to provide an explanation for Kohlrausch relaxation.

诺贝尔物理学奖得主菲利普·安德森将玻璃的性质和玻璃转变描述为物理学中最有趣的悬而未决的问题之一。尽管玻璃制造技术已经被人们知道和利用了数千年，但人们对液体如何以及为什么冷却到玻璃状而不是有序的结晶状态的了解相对较少。人们相信，通过研究原子在接近玻璃化转变时的动力学行为的演化，可以找到关于玻璃化转变本质的线索：尽管转变到有序状态伴随着指数依赖于时间的弛豫，但自从150多年前Kohlrausch的工作以来，人们已经知道无序和玻璃态系统以非指数形式松弛。尽管这种非(或延伸的)指数松弛似乎无处不在，但它的起源仍然存在争议。事实上，目前还不清楚它是来自平行的还是分级的过程，还是两者的组合。在某些方面，自旋玻璃是相对简单的模型系统，可以用来研究玻璃化行为。在自旋玻璃中，磁自旋的方向而不是它们的位置冻结为随机状态。我们最近对各种自旋玻璃的中子束和µ子束测量似乎表明，一种基于概率考虑的新理论可能会提供一个合适的模型来描述玻璃温度以上的驰豫。此外，我们还证明了该模型与最近基于合作无序或非扩展熵的热力学理论之间的联系，这些理论在描述地震和龙卷风等现象时也很有用。如果这种联系能够被证明，我们就有了一个方案，可以用它们的基本热力学性质来理解各种类型的自旋玻璃和结构玻璃(如脆弱玻璃和强玻璃)，并对其进行表征和参数描述。因此，这个提议的目的是使用中子自旋回波和Muon自旋弛豫技术来扩展我们对自旋玻璃的初步的、有限的概述，以严格检验新的概率松弛理论的适用性及其与非扩展熵理论的关系，以便建立一个理解玻璃转变的普遍热力学方法，并为Kohlrausch松弛提供解释。