Theory of complex oxides: superconductivity and interfaces

计算机、手机、医疗设备等现代技术之所以成为可能，是因为数十年来人们一直在努力制造更小、更快的电子设备。随着时间的推移，这种计算能力的指数增长被称为摩尔定律。当我们开始触及摩尔定律的基本极限时，人们对扩展纳米电子设备的能力越来越感兴趣。例如，在过去的十年里，人们对铁电和磁性材料进行了大量的基础研究，这些材料有一天可能会被整合到新的高速存储设备中。为此，研究正从传统的半导体转向新的材料家族。我的工作重点是过渡金属氧化物。过渡金属氧化物具有很大的潜力，因为它们具有许多特性——超导性、磁性、铁电性等——这些都是传统半导体所没有的。目前，需要回答的问题都是非常基本的：我们能否根据自然的基本定律来理解这些物质的行为？事实证明，许多过渡金属氧化物在有限的几何形状中（例如，纳米器件）与在大样本中具有不同的物理性质。我们能理解其中的原因吗？在我的研究中，我建立了计算机模型，基于基本的物理定律，模拟各种过渡金属氧化物的电子特性。通过这些模型，我希望解释简单氧化物结构（界面和异质结构）的物理性质，并了解杂质和缺陷所起的微妙作用。我的研究主要集中在两个材料家族：高温超导体和钛酸锶界面。这些家族中的第一个是在近30年前发现的，但在纳米尺度上出现的复杂自组织行为的新发现继续让我们感到惊讶。第二族在纳米电子学中有更直接的应用潜力，但也提出了关于电子在纳米尺度上的行为的问题；这里的基本目标是探索可以通过适当选择建筑材料和几何形状来设计成设备的广泛可能的特性。

Modern technology---computers, cell phones, medical equipment---is possible because of a decades-long push towards making smaller and faster electronic devices. This exponential growth of computing power over time is known as Moore's law. As we begin to bump up against fundamental limits to Moore's law, interest is growing in broadening the capabilities of nano-electronic devices. For example, the past decade has seen significant amounts of basic research devoted to ferroelectric and magnetic materials that might, one day, be incorporated into new high-speed memory devices. To this end, research is moving away from traditional semiconductors into new families of materials. My work focuses on transition metal oxides.Transition metal oxides hold a lot of potential because they can have many properties---superconductivity, magnetism, ferroelectricity, and others---that are not found in conventional semiconductors. At present, the questions that need to be answered are very basic: can we understand, in terms of the fundamental laws of nature, how these materials behave? It turns out that many transition metal oxides have different physical properties in confined geometries (for example, nanodevices) than they do in large samples. Can we understand why? In my research, I construct computer models, based on fundamental laws of physics, to simulate the electronic properties of various transition metal oxides. With these models, I hope to explain the physical properties of simple oxide structures (interfaces and heterostructures), and to understand the subtle role played by impurities and defects.My research focuses on two families of materials: high temperature superconductors and strontium titanate interfaces. The first of these families was discovered almost 30 years ago, but continues to surprise us with new revelations of complex self-organised behaviour that emerges on nanometre scales. The second family has more immediate potential for applications in nanoelectronics, but also raises questions about how electrons behave at the nanometre scale; here the fundamental goal is to explore the vast range of possible properties that can be engineered into devices by appropriate choice of building materials and geometry.