Nuclear Magnetic Resonance Study of Emergent Orders

摘要：在信息、传感和能源技术的先进应用中，寻找具有可控性能的新材料的技术驱动需要理解量子物质的新形式。量子材料研究的一个核心问题是研究强电子相关与自旋和轨道自由度的局部纠缠的综合效应，即所谓的自旋轨道耦合（SOC）。预测涌现性质是一个巨大的理论问题，因为SOC的存在意味着自旋不是一个好的量子数。现有的理论提出了大量奇异量子相的出现，可以通过局部电荷/轨道或局部自旋特性来区分。该奖项支持使用局部微观测量对这些涌现相进行广泛研究，旨在同时探测自旋、电荷/轨道和晶格性质。本研究的变革目标是确定一个适当的理论框架来描述具有强相关性和SOC的系统，从而促进具有设计特性的材料的发现。布朗大学和国家高磁场实验室的研究人员在对样品施加单轴应力、应变和外加磁场的同时，探测磁性和轨道/电荷性质，以调整相互作用。通过为研究生和本科生建立具有挑战性的训练场地，该项目嵌入了强大的教育成分，这些学生将参与科学，建模和技术开发。技术摘要：本研究项目主要利用核磁共振技术对具有显著自旋轨道耦合（SOC）的强相关电子系统中的涌现序进行实验研究，目的是破译导致物质涌现量子态的不同相互作用之间的复杂相互作用。这些核磁共振测量设计用于同时探测相关低能量下的自旋、电荷/轨道和晶格自由度，同时将样品置于对称破坏的单轴应力、应变和磁场中。为了实现这些目标，研究人员开发了一种基于表面线圈的新型核磁共振方法，以允许地应力和应变变化。研究的初期重点是铁基超导体模型系统。该团队在施加单轴应力和应变的实验条件下进行核磁共振，就像在传输性质的实验条件下一样。将这些发现联系起来，提供了电子液晶（向列）和磁态的微观性质的图像；多阶参数的共存及其相关波动在建立非常规超导性中的作用。为了提供对电子向列相固有特性的一般理解，这项工作从非常规超导体（掺杂莫特绝缘体）扩展到具有强SOC的磁性莫特绝缘体（例如5d电子双钙钛矿系统）。该研究的变革目标是了解具有局域电子和流动电子的系统中向列性的电子机制，并帮助确定一个适当的理论框架来描述相关和SOC具有可比能量尺度且两者都不能被扰动处理的系统。参与的研究生和本科生将在国家强磁场实验室获得宝贵的研究经验。

Non-Technical Abstract:The technological drive to find new materials with controllable desired properties for advanced applications in information, sensing, and energy technologies, requires understanding of the new forms of quantum matter. A central issue in quantum materials research is study of the combined effects of strong electronic correlations with local entanglement of spin and orbital degrees of freedom, so-called spin-orbit coupling (SOC). Predicting emergent properties represents a huge theoretical problem since the presence of SOC implies that the spin is not a good quantum number. Existing theories propose the emergence of a multitude of exotic quantum phases, distinguishable by either local charge/orbital or local spin properties. This award supports research on extensive study of these emergent phases using local microscopic measurements, designed to concurrently probe spin, charge/orbital, and lattice properties. The transformative goal of this research is to identify an appropriate theoretical framework for describing systems with both strong correlations and SOC and so promote the discovery of materials with designed properties. The researchers at Brown University and National High Magnetic Field Laboratory simultaneously probe magnetic and orbital/charge properties while subjecting the samples to uniaxial stress, strain, and applied magnetic field, to tune competing interactions. A strong educational component is imbedded in the project by establishing a challenging training ground for students, both graduate and undergraduate, who will be involved in the scientific, modeling, and technical developments. Technical Abstract:This research program focuses on the experimental investigation of emergent orders in strongly correlated electron systems with notable spin-orbit coupling (SOC) using nuclear magnetic resonance (NMR) techniques with the goal to decipher the complex interplay between different interactions that leads to the emergent quantum states of matter. These NMR measurements are designed to concurrently probe spin, charge/orbital, and lattice degrees of freedom at the relevant low energy, while subjecting the samples to symmetry-breaking uniaxial stress, strain, and magnetic field. To achieve these objectives, the researchers develop a novel NMR approach, based on the use of surface coils, to allow for both in-situ stress and strain variation. Initial emphasis of the research is on Fe-based superconductor model systems. The team performs NMR in the same experimental conditions of applied uniaxial stress and strain as those of transport properties. Correlating these findings provides a picture of the microscopic nature of electronic liquid crystals (nematic) and magnetic states; the coexistence of the multiple order parameters, and of the role their associated fluctuations play in establishing unconventional superconductivity. To provide general understanding of intrinsic properties of electronic nematic phases, this work extends from unconventional superconductors (doped Mott insulators) to the magnetic Mott insulators with strong SOC (e.g. 5d-electrons double perovskite systems). The transformative goal of the research is to understand electronic mechanism of nematicity in systems with both localized and itinerant electrons, and to help identify an appropriate theoretical framework for describing systems in which correlations and SOC are of comparable energy scale and neither can be treated perturbatively. The participating graduate and undergraduate students will gain valuable research experience at the National High Magnetic Field Laboratory.