Neutron Spin Echo and MuSR Studies of Glassy Dynamics

诺贝尔物理学奖获得者菲利普·安德森将玻璃的性质和玻璃化转变描述为物理学中最有趣的未解决的问题之一。尽管玻璃制造技术已经被发现和开发了数千年，但人们对液体如何以及为什么冷却到玻璃态而不是有序的结晶态的理解相对较少。人们相信，通过研究接近转变时原子动力学行为的演变，可以找到玻璃化转变性质的线索：而向有序状态的转变伴随着指数依赖于时间的弛豫，自Kohlrausch 150多年前的工作以来，人们已经知道无序和玻璃态系统的弛豫是非指数的。虽然这种非（或拉伸）指数松弛似乎是无处不在的，它的起源仍然存在争议。实际上，我们还不清楚它是由平行过程还是层次过程产生的，还是两者的结合。在某些方面，自旋玻璃是一种相对简单的模型系统，可以用来研究玻璃的行为。我们最近对各种自旋玻璃的中子和μ子束测量似乎表明，一种基于概率考虑的新理论可能提供一个合适的模型来描述玻璃温度以上的弛豫。此外，我们还证明了这个模型和最近的热力学理论的基础上合作的障碍，或非广泛的熵，这也是有用的，如地震和龙卷风的现象的特点之间的联系。如果这种联系能够得到证明，我们将有一个方案，通过它可以理解各种类型的自旋和结构玻璃（如易碎和坚固的玻璃），其特征和参数化的基本热力学性质。因此，本建议的目的是使用中子自旋回波和μ子自旋弛豫技术，以扩大我们的初步，有限的，调查自旋玻璃严格测试的适用性的新的概率弛豫理论和它的关系的理论，非广延熵，以建立一个通用的热力学方法来理解的玻璃化转变，并提供一个解释Kohlrausch松弛。

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.