Unconventional phase transitions and correlated dynamics in frustrated systems

凝聚态物理的主要目标之一是发现具有新颖和潜在有用性质的新材料。但是，由于这必须使用与“普通”物质相同的基本成分——质子、中子、电子来实现，新奇之处必须来自于它们如何组合，以及这些部分如何相互作用，从而形成一个不同的整体。即使它们的组成成分很简单，具有许多强相互作用部分的复杂系统也很难从理论上理解。因此，凝聚态物理的进步依赖于新的理论策略的发展，以理解复杂系统中大规模行为的出现，以及新的计算技术来模拟它们。最近人们认识到，寻找具有新特性的材料的一个很有希望的地方是在所谓的“受挫磁铁”中，这些系统被阻止，或至少被阻碍，形成我们熟悉的通常的磁性状态。在物理学中，挫折指的是不能同时满足的竞争相互作用的存在，并且发生在某些包含局部磁矩或自旋的材料中。最近特别令人感兴趣的例子是“自旋冰”，这是一类含有镝或钬的化合物。这些元素具有很强的磁性，例如用于计算机硬盘驱动器。自旋冰化合物中特殊的原子排列阻碍了这种磁性倾向，导致单个矩波动而不是形成有序结构的无序系统。自旋冰有许多有趣的特性，其中之一是据信它含有表现为磁单极子的粒子，这种粒子长期以来被推测为基本粒子，但从未被观察到。需要实验和理论工作来了解这些材料的性质，预测和发现它们可能承载的新现象，并将其扩展到其他相关系统。该项目将通过开发新的理论和计算技术来探索受挫系统的性质，包括受挫磁铁，如自旋冰。特别是，它们将通过相变进行研究，随着温度（或其他物理参数）的变化，例如从液态水到蒸汽的转变，会发生突然和戏剧性的行为差异。例如，在外部施加磁场的情况下，相变可以发生在受挫磁铁中，并且可以为许多受挫系统提供统一的视角。

One of the major goals of condensed matter physics is to discover new materials with novel, and potentially useful, properties. But since this must be achieved using the same basic constituents - protons, neutrons, electrons - as "ordinary" matter, the novelty must come from how they are combined, and the ways that the parts interact with each other, to give a different whole. Even when their constituents are simple, complex systems with many strongly interacting parts are difficult to understand theoretically. Progress in condensed matter physics therefore relies on the development of new theoretical strategies for understanding the emergence of large-scale behaviour in complex systems, as well as new computational techniques to simulate them.It has recently been appreciated that a promising place to look for materials with novel properties is in so-called "frustrated magnets", systems that are prevented, or at least hindered, from forming the usual magnetic states with which we are familiar. In physics, frustration refers to the presence of competing interactions that cannot simultaneously be satisfied, and occurs in certain materials containing localized magnetic moments, or spins.Examples of particular recent interest are the "spin ices", a family of compounds containing either dysprosium or holmium. These elements are highly magnetic, and are used for example in computer hard drives. The particular atomic arrangement in the spin ice compounds frustrates this magnetic tendency, leading to disordered systems where the individual moments fluctuate rather than forming an ordered structure. Among their many interesting properties, the spin ices are believed to host particles that behave as magnetic monopoles, long conjectured to exist as fundamental particles, but never observed. Both experimental and theoretical work is needed to understand the properties of these materials, to predict and discover new phenomena that they may host, and to extend this to other related systems.This project will explore the properties of frustrated systems, including frustrated magnets such as spin ice, by developing new theoretical and computational techniques. In particular, they will be studied through phase transitions, sudden and dramatic differences in behaviour that occur as temperature (or another physical parameter) changes, such as the transition from liquid water to steam. Phase transitions can occur in frustrated magnets in the presence, for example, of externally applied magnetic fields, and can provide a unifying perspective on a number of frustrated systems.