Synthetic Design of Kitaev Magnets and Spin Liquids

摘要：量子自旋液体是一种磁性材料，即使在接近绝对零度的温度下也不有序。量子自旋液体的理论非常丰富，预测了物质的奇异新状态，显示出不寻常的“分数化”激发。这种分数化的激发表现得好像它们是新型粒子。该项目旨在寻找一种表现出特定量子自旋液体行为特征的材料，这种行为特征是由理论家Alexei Kitaev在量子计算研究的背景下首次提出的。在这个项目中，基塔耶夫自旋液体物理是重要的，甚至是主导的新材料的设计。对所得性质进行了仔细的表征，结果将对广泛的可实现材料中的分数激发的性质产生深刻的见解，显着推进现代凝聚态物理前沿知识的状态。这个项目也奠定了一些必要的基础，为拓扑保护量子计算的可能的固态技术指明了道路。该项目还支持新课程“工程师量子力学”的课程开发，旨在帮助工科学生为未来从事量子技术发展的职业做好准备。技术摘要：该项目的研究目标是：(1)设计、发现和表征基塔耶夫物理在确定其磁性能方面发挥关键作用的新材料；(2)用非弹性中子散射研究新材料的自旋激发；(3)理解超出可解析基塔耶夫模型的模型哈密顿量的数据；(4)利用已有的知识对材料进行调整，改进材料设计原则，最终目标是找到具有基塔耶夫量子自旋液体基态的真实材料。将研究几种新的Kitaev材料的设计途径：(1)在石墨中插入三氯化钌；(2)利用离子交换反应取代蜂窝结构中的Ir和Rh，并用粉末中子衍射对这些反应进行原位研究；(3)三氯化锇的合成与晶体生长；蜂窝和超蜂窝杂化无机-有机骨架材料的合成。用x射线衍射、磁化和比热等基本工具对新材料进行了表征。将尝试通过化学掺杂和在某些情况下离子液体门控使一些材料金属化。有前途的材料将通过中子衍射和非弹性中子散射进行研究，以深入了解磁性基态和准粒子激发。从表征中获得的知识将用于帮助设计下一代材料。参与该项目的本科生将接受材料合成方面的培训；研究生将接受材料合成和中子散射两方面的训练。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

Nontechnical Abstract: Quantum spin liquids are magnetic materials which do not order even at temperatures approaching absolute zero. The theory of quantum spin liquids is very rich, with predictions of exotic new states of matter displaying unusual "fractionalized" excitations. Such fractionalized excitations behave as if they were new types of particles. This project seeks to find materials that show behavior characteristic of a particular kind of quantum spin liquid first proposed by the theorist Alexei Kitaev in the context of research on quantum computation. In this project new materials are designed in which Kitaev spin liquid physics is significant or even dominant. Careful characterization of the resultant properties is conducted, and the results will yield great insights into the nature of fractional excitations in a wide class of realizable materials, significantly advancing the state of forefront knowledge in modern condensed matter physics. This project also lays some necessary groundwork pointing the way to a possible solid-state technology for topologically protected quantum computing. This project also supports curriculum development of a new class, "Quantum Mechanics for Engineers", designed to help prepare engineering students for future careers in the development of quantum technologies. Technical Abstract: The research objectives of this project are to (1) design, discover, and characterize new materials in which Kitaev physics plays a crucial role in determining their magnetic properties; (2) study the spin excitations of the new materials with inelastic neutron scattering; (3) understand the data in the context of model Hamiltonians that go beyond the analytically soluble Kitaev model; and (4) use what has been learned to tune the materials and improve materials design principles, with the ultimate goal of finding a real material with a Kitaev quantum spin liquid ground state. Several design pathways to new Kitaev materials will be investigated: (1) intercalation of ruthenium trichloride into graphite; (2) use of ion-exchange reactions to replace Ir and Rh in honeycomb structures, and the investigation of these reactions in situ with powder neutron diffraction; (3) synthesis and crystal growth of osmium trichloride; and (4) synthesis of honeycomb and hyper-honeycomb hybrid inorganic-organic framework materials. The new materials are characterized with basic tools such as x-ray diffraction, magnetization, and specific heat. Attempts will be made to metallize some of the materials through chemical doping and in some cases ionic liquid gating. Promising materials will be studied with neutron diffraction and inelastic neutron scattering to gain an in-depth understanding of the magnetic ground state and quasiparticle excitations. The knowledge gained from characterization will be used to help design the next generation of materials. Undergraduate students involved in this project will be trained in materials synthesis; graduate students will be trained in both materials synthesis and neutron scattering.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.