Frustration and reduced dimensionality as routes to new forms of quantum order

当蒸汽冷却下来时，快速移动的水分子凝结成水。如果这些水被进一步冷却，水分子就会完全停止运动，并组织成美丽的晶体结构，我们称之为冰。我们用来制造电子设备的所有材料--例如你现在使用的计算机的半导体大脑--都含有液态或气态的移动的电子。那么当这些电子冷却下来的时候会发生什么呢？答案取决于它们所处物质的化学结构。在某些物质中，电子形成固体，就像冰中的水分子一样。有些人变得有磁性。而有些则成为超导体“--一种电阻率为零的非凡金属。这样的系统被认为表现出不同形式的秩序，也就是说，它们所包含的电子在冷却时以不同的方式组织自己。世纪材料科学的重要课题之一是研究电子呈现全新有序形式的材料。这是一个和寻找新类型基本粒子一样基本的问题。但这也是一个具有深远技术意义的问题，因为这些新材料有一天可能会被用来制造新形式的电子设备。这一提议结合了最先进的理论和实验，目的是探索新形式的量子秩序是如何在没有简单秩序形式的系统中出现的，而电子（很像人）面对着令人困惑的选择。我们考虑的实验系统处于现代材料科学的前沿，并且在物理行为方面是独特的。在LiV 2 O 4中，钒的d-电子变得和μ子一样重，在Na 4 Ir 3 O 8中，磁性Ir离子在任何温度下都不能磁性有序化。PrBa 2Cu 4 O 8是已知存在的最一维的金属，而有机化合物kappa-（ET）2Cu 2（CN）3和kappa-（ET）2Cu[N（CN）2]Cl，提供了一个长期寻求的在高度阻挫的三角晶格上实现量子自旋的方法。我们的主要实验方法将是测量这些系统如何传输热和电。在一定温度范围内测量的热导率和电导率之比是对给定材料中电子组织方式的非常敏感的测试。测量这个比率将使我们能够确定这些材料完全不同于传统的金属和绝缘体。我们还将研究它们的电子特性，如质量，如何随着系统变得更加沮丧而演变。与此同时，我们将使用超级计算机来解决非常规秩序如何在这些材料中工作的数学模型。特别是，我们试图了解电子如何一起工作，以形成新类型的基本激发“，例如粒子的一半电子的电荷！如果成功，这项工作有可能永远改变我们对金属的看法。

When steam cools down, fast-moving water molecules condense into water. And if this water is cooled further, the watermolecules stop moving altogether, and organize themselves into the beautiful crystal structures we know as ice. All ofthe materials we use to make electronic devices --- for example the semi-conductor brain'' of the computer you arenow using - contain mobile electrons in a liquid or gas-like state. So what happens to these electrons when they cooldown ? The answer depends on the chemical structure of material in which they live.In some materials the electrons form a solid, rather like the water molecules in ice. Some become magnetic. And somebecome superconductors'' - a remarkable type of metal whose electrical resistivity is exactly zero. Such systemsare said to exhibit different forms of order'', which is to say that the electrons they contain organize themselvesin different ways when they are cooled down. One of the most important themes in 21st century materials science is thesearch for materials whose electrons exhibit completely new forms of order. This is a problem as fundamental as thesearch for new types of elementary particle. But it is also one of profound technological significance, since thesenew materials may one day be used to build new forms of electronic device.This proposal combines state-of-the-art theory and experiment, with the goal of exploring how new forms of quantumorder can arise in systems where no simple form of order wins outright, and the electrons are frustrated (muchlike people) by the bewildering array of choices which they face. The experimental systems we consider are at the forefront of modern materials science, and are unique in their physical behaviour. In LiV2O4, vanadium d-electrons become as massive as muons.In Na4Ir3O8, magnetic Ir ions fail to order magnetically at any temperature. PrBa2Cu4O8 is the most one-dimensional metal known to exist, whilst the organic compounds kappa-(ET)2Cu2(CN)3 and kappa-(ET)2Cu[N(CN)2]Cl, provide a long-sought realization of quantum spins on a highly-frustrated triangular lattice.Our main experimental approach will be to measure how these systems transport heat and electricity. The ratio of thermal and electrical conductivities, measured over a range of temperatures, is a very sensitive test of the way in which the electrons in a given material have organized themselves. Measuring this ratio will enable us to establish that these materials are completely unlike conventional metals and insulators. We will also study how their electronic characteristics, such as mass, evolve as the systems become more frustrated. At the same time, we will use super-computers to solve mathematical models of how unconventional order might work in these and materials. In particular we try to understand how electrons work together to form new types of elementary excitation'', for example particles with half the charge of an electron ! If successful, this work has the potential to change how we think about metals forever...