Sr3Ru2O7: Quantum Nematic Fluid, Vector Magnetic Field Tuning and Spectroscopic Imaging Scanning Tunneling Microscopy

人们早就知道，如果你收集一组感觉到强大的相互作用力的粒子，并将它们设置得恰到好处，它们就可以形成有趣而美丽的图案。使用磁性铁屑作为粒子的桌子玩具和儿童游戏暗示了什么是可能的，而最近使用或多或少的标准光学显微镜已经可以观察到液晶中丰富的图案。在现代相互作用粒子研究的前沿是对某些特殊金属中所谓的“关联电子”的研究。在这里，相互作用是电磁力和一种被称为“泡利”或“交换”力的微妙量子机械力相结合的结果。在这样的材料中，可以想象到丰富的图案形成层次，有时被称为“量子自组织”。然而，想象这样的影响要比实际发现和观察它们容易得多，因为它们极其脆弱。为了观察它们，我们需要比十年前任何东西都更纯净的材料，绝对零度(零下273摄氏度)以内的温度，以及比光学显微镜强大数亿倍的显微镜。最近，我们已经能够推断出这种量子力学图案在一种特殊的氧化物金属Sr3Ru2O7中的存在。为了走到这一步，我们花了八年的时间才生长出世界上最高质量的晶体。我们现在有一个独特的机会来研究和确切地理解量子自组织是如何发生的。为了从中获利，我们构思了一个重大研究项目。首先，我们设计了一种特殊的“矢量磁铁”，它可以在计算机自动控制下产生沿我们定义的任何方向排列的巨大磁场。以前还没有制造过我们要求的规格的磁铁，但与一家专业公司合作的计算表明，它是可以做到的。利用这块磁铁，我们将能够描绘出新现象的性质，并优化它们发生的条件。除了帮助我们理解一些全新的东西外，这项研究还将与使用第二种独特设备--光谱成像扫描隧道显微镜(SI-STM)--的工作相结合。这台仪器是由我们中的一人(谢默斯·戴维斯)建造的，它可以以几乎难以想象的分辨率成像电子形成的图案。它对比单个原子直径小得多的距离很敏感，可以产生与我们将研究的新物理高度相关的信息，但不能通过任何其他实验技术获得。很少有材料有足够好的表面可以用SI-STM来研究，但我们已经通过12个月的可行性研究确定了Sr3Ru2O7是理想的。在进行我们提出的研究时，我们将回答一些基本的问题，关于现代物理学中最重要的问题之一--量子多体问题，以及先进的仪器技术(扩展现有的SI-STM并建立一个新的)。有人可能会争辩说，这些奖励本身就足够了，但它们并不是进行此类研究的唯一原因。从长远来看，继续推进支撑计算和数据存储的电子技术将要求我们使用相关的电子材料，这些材料是当今基础研究的主题。了解电子本身的自组织和模式对于这一更大的探索将是至关重要的。在像Sr3Ru2O7这样的材料中尤其如此，因为它们是化学上相似的过渡金属氧化物大家族的一部分，从长远来看，它们有望连接在一起，形成一种基于一套比今天半导体丰富得多的基本物理性质的技术。

It has long been known that if you take a collection of particles that feel strong mutual forces and set things up just right, they can form into intriguing and beautiful patterns. Desk toys and children's games using magnetic iron filings as the particles hint at what is possible, while more recently it has been possible to observe rich patterning in liquid crystals using more or less standard optical microscopy. At the forefront of modern research into interacting particles is the study of so-called 'correlated electrons' in some special metals. Here, the interactions are the result of combining electromagnetic forces with a subtle quantum mechanical force known as the 'Pauli' or 'exchange' force. A rich hierachy of pattern formation, sometimes called 'quantum self-organisation' can be imagined in such materials. However, imagining effects like these is much easier than actually discovering and observing them, because they are extremely fragile. To observe them, we need materials that are purer than anything that could be grown even a decade ago, temperatures within a few degrees of absolute zero (-273 degrees celsius) and microscopes that are hundreds of millions of times more powerful than optical ones.Very recently, we have been able to deduce the existence of such quantum mechanical patterning in a special oxide metal, Sr3Ru2O7. To even get this far, we had to work for eight years to grow the highest quality crystals in the world of it. We now have a unique opportunity to investigate and understand exactly how the quantum self-organisation takes place. To profit from this, we have conceived a major research project. First, we have designed a special 'vector magnet' which can produce an enormous magnetic field aligned along any direction that we define, under computer automated control. No magnet of our required specification has ever been built before, but calculations in collaboration with a specialist company show that it can be done. Using this magnet we will be able to map out the properties of the new phenomena, and optimise the conditions for them to occur.As well as helping us to understand something completely new, this study will be combined with work using a second unique piece of equipment, a Spectroscopic Imaging Scanning Tunneling Microscope (SI-STM). This instrument, built by the group of one of us (Seamus Davis), can image the patterns made by electrons with almost unimaginable resolution. It is sensitive to distances much less than the diameter of a single atom, and can yield information that is highly relevant to the new physics that we will study but cannot be obtained by any other experimental technique. Very few materials have good enough surfaces to be studied using SI-STM, but we have established that Sr3Ru2O7 is ideal by performing a 12 month feasibility study.In performing the research that we propose, we will answer some fundamental questions about the 'quantum many-body problem', one of the most important in modern physics, AND advance instrumentation technology (extending the existing SI-STM and building a new one). One might argue that these rewards are sufficient in their own right, but they are not the only reason for doing research like this. In the long term, continuing to advance the electronic technologies that underpin computation and data storage will require us to work with correlated electron materials that are the subject of today's fundamental research. Understanding self-organisation and patterning of the electrons themselves is going to be vital to that larger quest. This is especially true in materials like Sr3Ru2O7 because they are part of a large family of transition metal oxides which are chemically similar and have the promise, long-term, of being linked together to form a technology based on a far richer set of basic physical properties than is available using today's semiconductors.