Metal-insulator transitions and symmetry breaking in spin-orbit Mott materials

摘要：本项目的目标是研究凝聚态物理新前沿发现的晶体材料的电子和结构特性，在凝聚态物理中，材料既具有电子之间明显的相互作用，又具有其固有磁性（自旋）和轨道运动之间的强耦合。预计这种独特的能量尺度组合将稳定电子物质的基本新状态，从新形式的超导到具有量子计算长期应用潜力的新量子纠缠态。该项目支持的研究重点是了解实现这些新状态所需的材料途径，并探索负责驱动这些材料的原型母态-自旋轨道莫特相-从绝缘体到金属的相互作用。支持活动的工作是利用国家中子和x射线用户设施培训下一代科学家，以及通过支持新晶体材料的生长来解决国家在新材料发现/合成方面日益增长的赤字。该项目通过暑期研究实习为未被充分代表的本科生提供研究经验，并开展旨在激励大学预科学生追求材料科学/物理学术和职业道路的外展活动。技术摘要：该项目着重于实验探索新型自旋轨道Mott （SOM）材料通过载流子/带宽调谐从其母体绝缘状态驱动到金属状态的机制。SOM系统的绝缘相位是由强自旋轨道耦合、晶体场和短程库仑相互作用之间的微妙相互作用驱动的。SOM化合物中这种独特的能量尺度平衡被预测会产生附近的奇异基态，从高温超导到新型量子自旋液体，再到相关的拓扑相。这些新阶段的模型将它们放置在接近父SOM状态的位置。该项目的主要目标是了解一旦这种母态不稳定并被驱动到附近的材料相空间中，相互作用是如何演变的——具体来说，是解决电子相关性的作用以及电子和结构自由度在接近金属态时的演变。寻找自旋轨道Mott相熔化之外的新态/相行为是支持研究的第二个重叠目标。研究活动包括综合材料合成、体电子特性表征和中子/x射线散射，旨在形成Ruddlesden-Popper、焦绿盐和几何受挫铱酸盐类受扰SOM态相互作用的全面图景。研究生和本科生将接受材料合成技术以及在国家用户设施中使用中子和x射线散射的训练，帮助建立下一代国家用户社区的核心。

Nontechnical Abstract:The goal of this project is to study the electronic and structural properties of crystalline materials found at a new frontier of condensed matter physics, one where materials possess both an appreciable interaction between electrons in tandem with a strong coupling between their inherent magnetism (spin) and their orbital motion. This unique combination of energy scales is predicted to stabilize fundamentally new states of electronic matter, ranging from new forms of superconductivity to new quantum entangled states with far-term applications potential in quantum computing. Research supported by the project focuses on understanding the materials pathways necessary for realizing these new states and on exploring the interactions responsible for driving the prototypical parent state of these materials - the spin-orbit Mott phase - from an insulator into a metal. Supported activities work to train the next generation of scientists utilizing national neutron and x-ray user facilities as well as work to address the nation's growing deficit in new materials discovery/synthesis by supporting the growth of new crystalline materials. The project provides research experience to undergraduates from underrepresented demographics through summer research internships as well as conducts outreach activities aimed at inspiring precollege students to pursue materials science/physics academic and career pathways. Technical Abstract:The project focuses on experimentally exploring the mechanisms through which new classes of spin-orbit Mott (SOM) materials are driven from their parent insulating states into the metallic regime via carrier/bandwidth tuning. The insulating phases of SOM systems are inherently driven by a delicate interplay between strong spin-orbit coupling, crystal field, and short-range Coulomb interactions. This unique balance of energy scales in SOM compounds is predicted to host nearby exotic ground states ranging from high temperature superconductivity, to novel forms of quantum spin liquids, to correlated topological phases. Models of these new phases place them within close proximity to the parent SOM state. The primary goal of the project is to understand how interactions evolve once this parent state is destabilized and driven into nearby materials phase space - specifically, to resolve the role of electron correlations and the evolution of electronic and structural degrees of freedom as the metallic state is approached. Searching for new states/phase behaviors beyond the melting of the spin-orbit Mott phase is a second, overlapping goal of the supported research. Research activities are comprised of a combined materials synthesis, bulk electron properties characterization, and neutron/x-ray scattering effort aimed at forming a comprehensive picture of interactions in perturbed SOM states in classes of Ruddlesden-Popper, pyrochlore, and geometrically frustrated iridates. Students at the graduate and undergraduate levels will be trained in materials synthesis techniques as well as in the use of neutron and x-ray scattering at national user facilities, helping to build the core of the next generation of the national user community.