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成为现代生活中不可或缺的一部分，其性能、尺寸、能耗等方面都在逐年提高。在这些设备中是具有特殊电子特性的材料，如半导体和磁铁。它们的特性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，正如20世纪初所阐明的那样。现在在21世纪，人们越来越倾向于使用基于更复杂效应的新一代量子技术，例如在量子计算机中，多个量子态的相关或纠缠。这些发展的基础是寻找新的量子材料，在这些材料中，电子-电子相关会产生纠缠或相关的基态，如原子自旋、轨道或电荷态的长程顺序，或像超导体和量子自旋液体（QSLs）这样的类流体态，其中许多可能的成对量子态是叠加的。近年来，拓扑效应已被用于发现更多类型的量子材料，通过诸如基塔耶夫耦合这样的效应，它取决于材料内成对磁相互作用的方向。该项目旨在利用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杰出的物理和化学性质，通常是其领域中最好的，例如铁电性BaTiO3， YBa2Cu3O7高tc超导体，用于自旋电子学的（La,Sr）MnO3和Sr2FeMoO6 CMR（巨磁阻），多铁性BiFeO3和混合导体，如用于燃料电池的掺杂LaCrO3。我们将以重过渡金属为基础的钙钛矿为目标，这些钙钛矿具有小自旋的电子态，这可以放大量子行为，并且自旋轨道耦合强，从而在属性中产生强各向异性（局部方向性），从而增强拓扑影响。像Sr2FeMoO6中的Fe/Mo这样的阳离子的化学排序，被称为双钙钛矿衍生物，将用于创建有趣的网络拓扑，这种网络拓扑往往会挫败简单的“上下”磁顺序，使量子波动更占主导地位。高压（HP）合成方法将被使用，因为这些方法对于稳定钙钛矿型材料是有效的，并且也可以在基本ABO3排列中产生阳离子有序网络。概念验证实验表明，在HP上可以在钙钛矿B位点上产生1:1或1:2顺序的阳离子，也可以在A位点上产生1:1顺序的过渡金属和其他类型的阳离子。我们发现的“双双钙钛矿”排列甚至有1:1的A和B位点顺序，例如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（1gpa = 10,000个大气压）才能显著改变其化学、结构和性能。我们能够达到22 GPa的压力（而许多早期甚至现在的团队只能达到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团队合作，制造其他类型的氧化物和氮化物材料，这些材料显示出有趣和有用的磁性、催化性和与能源相关的特性。

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.