Emergence of novel electronic states in 5d transition metal oxides

在寻找具有新现象的材料的过程中，包括在技术应用中具有开发潜力的材料，最近的焦点落在自旋轨道相互作用的作用上。这是一种相对论性的相互作用，它将电子的固有自旋与它的轨道角动量耦合在一起。通常情况下，自旋轨道相互作用对材料电子性质的影响很小，可以将其视为弱扰动来考虑。然而，自旋轨道相互作用随着原子序数Z的增加而迅速增加（与Z的四次方成正比），对于较重的原子，特别是具有未填充5d轨道的第三行过渡金属原子，其强度与决定材料电子性质的其他相互作用相当。据预测，相似强度相互作用之间的竞争将导致5d化合物中物质的新涌现状态，这是以前从未观察到的。在这个项目中，我们将合成和研究几个家族的5d过渡金属氧化物的基本性质。在过去的几年里，激烈的理论活动已经产生了许多关于这些材料的预测。一种预测是称为拓扑莫特绝缘体的相，其稳定性归功于强自旋轨道相互作用引起的电子带的有趣拓扑性质。其他预测包括，热驱动的金属绝缘体转变，非常规的高温超导性，以及所谓的自旋液态，这种状态具有尚未发现的紧急激发，称为马约拉纳费米子。从实验的角度来看，5d过渡金属氧化物的探索相对较少，这主要是因为很难制作出高质量的单晶样品。我们的提案旨在整合成功的研究计划所需的所有必要组成部分。将共同努力，以制备纯、高质量的单晶形式感兴趣的材料。在我们的家庭实验室中，将使用设备对其电学、热学和磁性进行完整的表征。有了最好的样品，我们将利用同步加速器x射线技术的最新进展来探测预计存在于5d氧化物中的新型自旋轨道态。这项工作将与牛津郡的钻石光源和格勒诺布尔的欧洲同步辐射设施等大型设施的同事合作完成。最后，我们将与理论家密切合作，对我们发现的新电子态进行全面的理解。

In the fascinating search for materials which display new phenomena, including materials with potential for exploitation in technological applications, the spotlight has recently fallen on the role of the spin-orbit interaction. This is a relativistic interaction which couples the electron's intrinsic spin to its orbital angular momentum. Normally, the effect of the spin-orbit interaction on the electronic properties of materials is minimal and can be taken into account by treating it as a weak perturbation. However, the spin-orbit interaction increases rapidly with atomic number Z (in proportional to Z to the fourth power), and for heavier atoms, especially third row transition-metal atoms with unfilled 5d orbitals, it is comparable in strength with the other interactions that determine the electronic properties of materials. The resulting competition between interactions of similar strength is predicted to result in new emergent states of matter in 5d compounds which have never been observed before.In this project we shall synthesise and investigate the fundamental properties of several families of 5d transition-metal oxides. Intense theoretical activity over the last few years has produced a number of predictions for these materials. One predictions is of phases called topological Mott insulators which owe their stability to an interesting topological property of the electron bands caused by the strong spin-orbit interaction. Other predictions include, thermally-driven metal-insulator transitions, unconventional high temperature superconductivity, and so-called spin-liquid states which have as-yet undiscovered emergent excitations called Majorana fermions. 5d transition metal oxides have been relatively unexplored from an experimental point of view, largely because of the difficulty to make good quality single crystal samples. Our proposal is designed to integrate all of the necessary components required for a successful research programme. A concerted effort will be made to prepare materials of interest in the form of pure, high-quality, single-crystals. Complete characterisation of their electrical, thermal and magnetic properties will be undertaken using equipment in our home laboratories. Armed with the best possible samples we will exploit spectacular recent advances in synchrotron X-ray techniques to probe the novel spin-orbital states predicted to exist in 5d oxides. This work will be performed partly in collaboration with colleagues at large-scale facilities such as the Diamond Light Source in Oxfordshire, and the European Synchrotron Radiation Facility in Grenoble. Finally, we shall work closely with theorists to develop a comprehensive understanding of the novel electronic states we discover.