New Quantum Materials from High Pressure Synthesis

手机、平板电脑和笔记本电脑等电子技术已经成为现代生活中不可或缺的一部分，性能、尺寸、能源消耗等方面的改进都在逐年提高。在这些设备中是具有特殊电子性能的材料，如半导体和磁体。正如20世纪初阐明的那样，它们的特征和性能在很大程度上受到单个或几个电子的量子力学行为的限制。如今，在21世纪，人们越来越倾向于使用基于更复杂的效应的新一代量子技术，例如在量子计算机中的多个量子态的关联或纠缠。在这些发展的背后是寻找新的量子材料，其中电子-电子关联引起纠缠或关联的基态，例如原子自旋、轨道或电荷态的长程顺序，或者像超导体和量子自旋液体(QSL)这样的流体状态，其中许多可能的成对量子态被叠加在一起。近年来，拓扑效应被用来发现更多类型的量子材料，通过Kitaev耦合效应，这种耦合依赖于材料内部成对磁相互作用的方向。本项目旨在通过高压反应方法合成钙钛矿氧化物家族中的新量子材料。钙钛矿氧化物具有基于矿物CaTiO3的ABO3排列的结构。它们具有巨大的化学和结构灵活性以及优异的物理和化学性质，这些性能在各自的领域中往往是最好的，例如铁电BaTiO_3，YBa2Cu3O_7高T_c超导体，用于自旋电子的(La，Sr)MnO_3和Sr2FeMoO_6 CMR(巨磁电阻)，多铁BiFeO_3，以及用于燃料电池的掺杂LaCrO_3等混合导体。我们将以钙钛矿为目标，这些金属的重过渡金属具有小自旋的电子态，这放大了量子行为，以及强烈的自旋-轨道耦合，导致在突出拓扑影响的性质中产生强烈的各向异性(局部方向性)。阳离子的化学有序，如在Sr2FeMoO6中的Fe/Mo，被称为双钙钛矿衍生物，将被用来创建有趣的网络拓扑，这种拓扑往往会阻碍简单的向上-向下的磁有序，使量子涨落更占优势。高压(HP)合成方法将被使用，因为这些方法被认为是稳定钙钛矿型材料的有效方法，也可以在基本的ABO3排列中生成阳离子有序网络。概念验证实验表明，在钙钛矿B位上可以产生1：1或1：2级的阳离子，在A位上也可以产生1：1级的过渡金属和其他类型的阳离子。我们发现的一种双双钙钛矿结构甚至具有1：1的A和B位序，如CaMnFeReO6，因此为发现新的量子材料提供了许多排列。氧化物材料是不可压缩的，因此需要Gpa级的压力(1 Gpa=10,000个大气压)才能显著改变它们的化学、结构和性能。我们能够承受高达22 Gpa的压力(而许多早期甚至现在的群体只能达到6-8 Gpa)，这将使我们能够发现这些新材料。我们还将与外部合作伙伴小组合作，制造其他类型的氧化物和氮化物材料，这些材料具有有趣和有用的磁性、催化和能源相关特性。

Electronic technologies such as mobile phones, tablets and laptops have become indispensable to modern life, with improvements in performance, size, energy-consumption etc. occurring year-on-year. Within these devices are materials with particular electronic properties such as semiconductors and magnets. Their characteristics and performance are largely limited by the quantum mechanical behaviour of single or a few electrons, as elucidated in the early 20th century. Now in the 21st century there is an increasing drive towards the use of a new generation of quantum technologies based upon more sophisticated effects such as the correlation or entanglement of multiple quantum states, e.g. in a quantum computer.Underlying these developments is the search for new quantum materials where electron-electron correlation gives rise to entangled or correlated ground states such as long range orders of atomic spin, orbital, or charge states, or fluid-like states like superconductors and quantum spin liquids (QSLs) in which many possible paired quantum states are superimposed. Topological effects have been used to discover further types of quantum material in recent years, through effects such Kitaev coupling which depends upon the directions of pairwise magnetic interactions within a material.This project aims to synthesise new quantum materials within the family of perovskite oxides using high pressure reaction methods. Perovskite oxides have structures based on the ABO3 arrangement of the mineral CaTiO3. They have enormous chemical and structural flexibility as well as outstanding physical and chemical properties, which are often the best in their field, e.g. ferroelectric BaTiO3, YBa2Cu3O7 high-Tc superconductor, (La,Sr)MnO3 and Sr2FeMoO6 CMR (colossal magnetoresistance) for spintronics, multiferroic BiFeO3, and mixed conductors such as doped LaCrO3 for fuel cells. We will target perovskites based on heavy transition metals with electronic states that have small spins, which amplifies quantum behaviour, and strong spin-orbit coupling that gives rise to strong anisotropy (local directionality) in properties that accentuate topological influences. Chemical ordering of cations like that of Fe/Mo in Sr2FeMoO6, known as a double perovskite derivative, will be used to create interesting network topologies that tend to frustrate simple 'up-down' magnetic orders, making quantum fluctuations more dominant.High pressure (HP) synthesis methods will be used as these are known to be effective for stabilising perovskite type materials, and also for generating cation ordered networks within the basic ABO3 arrangement. Proof of concept experiments have shown that 1:1 or 1:2 orders of cations on the perovskite B sites, and also 1:1 ordering of transition metal and other types of cation at A sites can be generated at HP. A 'double double perovskite' arrangement we discovered even has 1:1 A and B site orders, e.g. CaMnFeReO6, and so offers many permutations for discovery of new quantum materials. Oxide materials are incompressible so GPa-scale pressures (1 GPa = 10,000 atmospheres) are needed to change their chemistry, structures and properties significantly. Our ability to reach pressures up to 22 GPa (whereas many early and even present-day groups can only access 6-8 GPa) will enable us to discover these new materials. We will also collaborate with external partner groups to make other types of oxide and nitride materials that show interesting and useful magnetic, catalytic, and energy-related properties.