NMR Studies of Organic and Inorganic Frustrated Quantum Magnets

非技术摘要本项目由材料研究部的凝聚态物理计划资助，属于磁性材料领域。 无序的基态被假定出现在磁系统中，其中自旋被安排在特定的挫折几何形状。长期以来，这些所谓的自旋液相具有在量子计算技术中使用的潜力，并被提议作为高温超导性的途径。然而，这些候选材料只是最近才通过实验实现的。由几何形状决定的竞争相互作用被认为是其稳定性的重要组成部分，但真实的系统如何依赖于细节仍不清楚。 本研究项目旨在通过利用与几何结构相关的相互作用的微妙平衡，探索受抑量子磁体的无序和有序基态的稳定性。 调谐是通过改变应变、压力和磁场强度来实现的。所访问的相位和相关联的激励的性质通过测量的组合来确定，相当大程度上依赖于固态磁共振技术。 该项目的目标是实现与科学教育和培训的研究生和本科生在国家重要的技术领域，包括高频和磁共振技术，以及高压和低温instrument.Technical abstractionThis项目需要使用固态磁共振技术探测性能的挫折量子磁体和场诱导非均匀超导。 关于量子磁体，长程有序和量子无序系统之间的对比特别令人感兴趣，基态的性质，激发光谱以及磁场或应变调谐的影响也是如此。 所选的研究材料可分为两类。第一种包括两种结构相似的无机化合物，它们表现出反铁磁（AF）和无序基态。 第二组包括两个有机各向异性三角系统。 两者的基态都可以通过施加单轴应变或压力来连续调节。 重点是与磁有序或自旋能隙相的抑制相关的物理性质的演变。 相变的签名，激发的性质，将推断从NMR光谱和弛豫测量。干净的层状超导体是场致超导相的理想候选者。研究所选的系统是已知的弱耦合层，并且很容易获得适当的场范围。 磁共振通常是这些问题的理想探针，因为它与所需的极端条件相兼容，并且因为它是通过超精细相互作用对电子环境敏感的局部探针。 研究将在P.I.的实验室进行。在加州大学洛杉矶分校，并在国家高磁场实验室（NHMFL）的领域大于什么是当地可用的。

Non-technical abstractThis project, supported by the Condensed Matter Physics Program in the Division of Materials Research, is in the area of magnetic materials. Disordered ground states are postulated to arise in magnetic systems where the spins are arranged in specific frustrated geometries. Long sought-after, these so-called spin liquid phases have the potential for use in quantum computation technology and are proposed as a route to high temperature superconductivity. However, candidate materials for these were experimentally realized only recently. Competing interactions, determined by geometry, are understood as an important component for their stability, but how the real systems are dependent on the details remains unclear. This research project aims to explore the circumstances for stability of disordered and ordered ground states of frustrated quantum magnets by exploiting the delicate balance of interactions linked to the geometry. Tuning is accomplished by means of varying strain, pressure, and magnetic field strength. The nature of the accessed phases and associated excitations are determined by a combination of measurements, with considerable reliance on solid state magnetic resonance techniques. The project goals are achieved in tandem with the science education and training of graduate students and undergraduate students in nationally important technical fields, including high frequency and magnetic resonance techniques, as well as high pressure and cryogenic instrumentation.Technical abstractThis project entails the use of solid state magnetic resonance techniques to probe the properties of frustrated quantum magnets and field-induced inhomogeneous superconductivity. With respect to the quantum magnets, the contrast between long-range ordered and quantum disordered systems is of particular interest, as are the nature of the ground states, the spectrum of excitations, and the effects of tuning by magnetic field or strain. The materials selected for study can be classified into two groups. The first includes two structurally similar inorganic compounds, which exhibit antiferromagnetic (AF) and disordered ground states. The second group includes two organic anisotropic triangular systems. The ground states of both are continuously tunable by the application of uniaxial strain or pressure. The focus is on the evolution of physical properties associated with the suppression of magnetically ordered or spin-gapped phases. Signatures for phase transitions, and the nature of excitations, will be inferred from NMR spectroscopy and relaxation measurements. Clean and layered superconductors are ideal candidates for field-induced superconducting phases. The system chosen for study is known for weakly-coupled layers, and the appropriate field range is easily accessed. Magnetic resonance is often an ideal probe for these problems, because of its compatibility to the required extreme conditions, and because it is a local probe sensitive to the electronic environment through the hyperfine interaction. The research will be conducted in the laboratory of the P.I. at UCLA, and at the National High Magnetic Field Laboratory (NHMFL) for fields larger than what is available locally.