New correlated electronic states arising from strong spin-orbit coupling

磁现象遍及我们周围的世界，并被用于各种各样的实用设备，从纳米级数据存储设备到电动机再到等离子体聚变反应堆。在基本层面上，固体中的磁性来自许多原子磁体的协调作用。原子磁性来源于电子的自旋和轨道运动，自旋和轨道磁性的相对重要性取决于特定的磁性原子及其环境。这个项目关注的是含有重金属原子（如钌、钼、锇和铼）的氧化物的磁性。这些原子部分填充了4d或5d电子轨道，具有较大的自旋-轨道相互作用，强烈地纠缠着自旋和轨道磁性。直到最近，在强自旋轨道耦合存在下的磁性研究仅限于f电子系统，但今天有越来越多的关注于4d和5d系统，其中更大的电子迁移率导致更多样化的现象范围。在过去的几年里，对于具有强自旋轨道耦合的磁系统出现了大量的理论预测，但很少得到经验证实。这些预测包括：(i)原子在孤立状态下没有磁性，但通过与邻近原子的相互作用产生磁性的材料，（ii）各向异性、键定向磁耦合导致新的传播磁模式，（iii）量子力学纠缠的自旋和轨道液态具有外来涌现的准粒子激发，（iv）自旋轨道增强磁相关性驱动的金属-绝缘体跃迁，(v)掺杂电子在磁波动介导下的非常规超导性。研究计划旨在寻找和研究4d和5d氧化物中的这些和其他新型磁相。一个重大的挑战将是高质量单晶的生长，这是实验中必不可少的样品。为了克服这一挑战，我们聚集了两个具有大量相关专业知识的领先晶体种植者，以及项目合作伙伴Yamaura教授，他带来了高压合成的额外能力。我们将在国际同步加速器和中子设施中使用最先进的技术进行测量，以探测感兴趣的材料中的新型自旋轨道态。我们将与设施的工作人员合作，包括我们的项目合作伙伴钻石光源和保罗谢勒研究所，以及格勒诺布尔的欧洲同步辐射设施和ISIS散裂中子源，进行测量和开发必要的技术。最后，我们将与多伦多大学的理论项目伙伴和合作者合作，详细了解我们将发现的新电子和磁态。

Magnetic phenomena pervade the world around us and are used in a huge variety of practical devices, ranging from nanoscale data storage devices through electric motors to plasma fusion reactors. At a fundamental level, magnetism in solids comes from the coordinated actions of many atomic magnets. The atomic magnetism originates from the intrinsic spin and the orbital motion of the electrons, and the relative importance of spin and orbital magnetism depends on the particular magnetic atom and its environment. This project concerns magnetism in oxides containing heavy metal atoms such as ruthenium, molybdenum, osmium and rhenium. These atoms have partially filled 4d or 5d electronic orbitals with a large spin-orbit interaction which strongly entwines the spin and orbital magnetism. Until recently, the study of magnetism in the presence of strong spin-orbit coupling was confined to f-electron systems, but today there is increasing focus on 4d and 5d systems, in which the greater mobility of the electrons results in a more diverse range of phenomena. In the past few years, a large number of theoretical predictions have appeared for magnetic systems with strong spin-orbit coupling, but very few have been confirmed empirically. The predictions include: (i) materials whose atoms have no magnetism when in isolation but develop magnetism through interactions with neighbouring atoms, (ii) anisotropic, bond-directional magnetic couplings resulting in novel propagating magnetic modes, (iii) quantum-mechanically entangled spin and orbital liquid states with exotic emergent quasiparticle excitations, (iv) metal-insulator transitions driven by spin-orbit enhanced magnetic correlations, and (v) unconventional superconductivity of doped electrons mediated by magnetic fluctuations. The programme of research aims to search for and study these and other novel magnetic phases in 4d and 5d oxides. A significant challenge will be the growth of high quality single crystals, which are essential as samples for the experiments. To overcome this challenge we have assembled two leading crystal growers with a vast amount of relevant expertise, as well as a Project Partner, Prof Yamaura, who brings additional capability in high pressure synthesis. We shall perform measurements to probe the novel spin-orbital states in the materials of interest using state-of-the-art techniques at international synchrotron and neutron facilities. We shall collaborate with staff at the facilities, including our Project Partners the Diamond Light Source and Paul Scherrer Institute, as well as the European Synchrotron Radiation Facility in Grenoble and the ISIS spallation neutron source, to perform the measurements and develop the necessary techniques. Finally, we shall work with our theory Project Partners at the University of Toronto and collaborators to develop a detailed understanding of the new electronic and magnetic states we will uncover.