Unconventional phase transitions and correlated dynamics in frustrated systems

凝聚态物理学的主要目标之一是发现具有新颖且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，所以新奇之处必须来自它们如何组合，以及各部分相互作用的方式，以产生不同的整体。即使它们的组成部分很简单，但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，凝聚态物理学的进展依赖于新的理论策略的发展，以理解复杂系统中大尺度行为的出现，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有希望的地方是所谓的“受抑磁体”，即被阻止或至少被阻碍的系统，形成我们所熟悉的通常的磁性状态。在物理学中，阻挫是指存在相互竞争的相互作用，而这些相互作用不能同时得到满足，并且发生在某些包含局部磁矩或自旋的材料中。最近特别感兴趣的例子是“自旋冰”，一个包含镝或钬的化合物家族。这些元件具有高磁性，例如用于计算机硬盘驱动器。自旋冰化合物中的特殊原子排列阻碍了这种磁性趋势，导致无序系统，其中单个磁矩波动而不是形成有序结构。在它们的许多有趣的特性中，自旋冰被认为是具有磁单极子行为的粒子，长期以来一直被认为是基本粒子，但从未被观察到。为了理解这些材料的性质，预测和发现它们可能存在的新现象，并将其扩展到其他相关系统，需要进行实验和理论工作。本项目将通过开发新的理论和计算技术，探索包括自旋冰等受抑磁体在内的受抑系统的性质。特别是，他们将通过相变，突然和戏剧性的行为差异，发生温度（或另一个物理参数）的变化，如从液态水到蒸汽的过渡进行研究。相变可以发生在受抑磁体的存在下，例如，外部施加的磁场，并可以提供一个统一的角度对一些受抑系统。

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.