Quantum Phases in spin-orbit coupled honeycomb magnets: beyond 4d and 5d transition metal ions

非技术摘要：物质的量子相是基于被限制在晶格中的电子之间的纠缠。这种相的一个熟悉的例子是超导；这种曾经奇特的现象现在已经成熟，并被用于磁共振成像（MRI）等技术应用。同样，在蜂窝晶格磁体（即由六边形组成的晶格结构构成的磁体）的研究中，正在探索的物质的新量子相可以提供戏剧性的技术成果。一种预测的量子相，基塔耶夫蜂巢量子自旋液体，支持特殊的激发态，可以形成量子计算中异常强大的“量子比特”。这个研究项目旨在利用以前未被探索过的磁性离子，在新的蜂窝晶格材料中产生这种奇特的相。本科研究人员，他们准备样品并执行磁性表征的基本技术，开展了研究的大部分探索性方面。参与该项目的研究生掌握单晶生长、热力学表征和非弹性中子散射的技术。这个项目在很大程度上依赖于美国的大型中子科学设施。技术摘要：本研究旨在利用非常规材料选择产生新的物质量子相。具有强自旋轨道耦合的磁绝缘体是探索基于量子纠缠的各种有趣相的理想目标，例如量子自旋液体。这些奇异相承载着潜在有用的准粒子激发；一个例子是基塔耶夫蜂窝量子自旋液体预测的“任意子”激发。任何子，一旦它们在真实的材料中被成功地制造出来，就可以用于拓扑保护的量子计算。形成这种奇异相的两个关键因素是：1)蜂窝晶格上的各向异性磁相互作用，可以从具有强自旋-轨道耦合的磁性物质中获得；2)量子涨落，这是相关伪自旋1 / 2磁矩的自然特征。这些成分之前已经在基于4d和5d过渡金属离子的蜂窝晶格材料中被寻找。目前的研究项目将搜索范围扩展到这些系列之外的磁性物质的非常规选择，使更广泛的表征技术成为可能，同时开辟了一个新的材料领域。固态合成方法，包括强烈的晶体生长努力，与使用热力学探针和低至50 mK的非弹性中子散射对材料进行详细表征相结合。本科研究人员准备样品并执行磁性表征的基本技术，开展了研究的大部分探索性方面。参与该项目的研究生掌握单晶生长、热力学表征和非弹性中子散射的技术。这个项目在很大程度上依赖于美国的大规模中子科学设施。

Non-Technical Abstract:Quantum phases of matter are based on entanglement between electrons confined to crystal lattices. A familiar example of such a phase is superconductivity; this once-exotic phenomenon has now matured and is being used for technological applications such as Magnetic Resonance Imaging (MRI). Similarly, the new quantum phases of matter being explored in this research on honeycomb lattice magnets (i.e., magnets built from a lattice structure composed of hexagons) could provide dramatic technological consequences. One predicted quantum phase, the Kitaev Honeycomb Quantum Spin Liquid, supports special excited states that could form unusually robust "qubits" for quantum computations. This research project aims to produce such exotic phases in new honeycomb lattice materials, using previously unexplored choices of magnetic ions. Undergraduate researchers, who prepare samples and perform basic techniques for magnetic characterizations, carry out a large part of the exploratory aspects of the research. Graduate students involved in this project master techniques in single crystal growth, thermodynamic characterization, and inelastic neutron scattering. This project heavily relies on large-scale neutron science facilities in the United States.Technical Abstract:This research is designed to produce new quantum phases of matter using unconventional materials choices. Magnetic insulators with strong spin-orbit coupling are ideal targets for exploring a wide variety of interesting phases based on quantum entanglement, such as Quantum Spin Liquids. These exotic phases host potentially useful quasi-particle excitations; one example is the "anyon" excitation predicted for the Kitaev Honeycomb Quantum Spin Liquid. Anyons, once they are successfully produced in a real material, could be used for topologically protected quantum computations. The two key ingredients for exotic phases like this are 1) anisotropic magnetic interactions on the honeycomb lattice, obtainable from magnetic species with strong spin-orbit coupling, and 2) quantum fluctuations, which are a natural feature of correlated pseudo-spin ½ magnetic moments. These ingredients have previously been sought in honeycomb lattice materials based on 4d and 5d transition metal ions. The current research project extends the search to unconventional choices of magnetic species outside of these series, enabling a wider variety of characterization techniques while opening a new arena of materials to be explored. Solid-state synthesis methods, including intense crystal growth efforts, are combined with detailed characterizations of materials using thermodynamic probes and inelastic neutron scattering at temperatures as low as 50 mK. Undergraduate researchers, who prepare samples and perform basic techniques for magnetic characterizations, carry out a large part of the exploratory aspects of the research. Graduate students involved in this project master techniques in single crystal growth, thermodynamic characterization, and inelastic neutron scattering. This project heavily relies on large-scale neutron science facilities in the US.