DMREF: Collaborative Research: Emergent Functionalities in 3d/5d Multinary Chalcogenides and Oxides

这个研究项目的重点是理解和扩大在元素周期表底部的原子起重要作用的材料类别。含有这些元素的晶体化合物具有一系列相互关联的特性，包括电子运动和自旋之间的强耦合、不寻常的磁性行为、更宽的电子能带以及相邻原子成对吸引的倾向。特别关注包括碲在内的层状材料的探索，因为它们显示出各种各样的结构图案。第一性原理计算方法用于研究本课程的候选材料，确定那些最有希望作为定向合成和深入实验研究目标的材料。理论与实验之间的比较提供了反馈，以重新集中理论和计算工作。该团队提供散装和薄膜材料生长的能力，并使用光学、散射和扫描探针技术进行表征。该活动通过本科生参与研究、与新泽西州自由科学中心的外展项目协调以及组织专题研讨会和会议提供教育机会。技术摘要近年来，随着硬磁体、拓扑绝缘体、多铁体、超导体和热电学等领域的科学进步和应用，对5d材料和3d/5d杂化材料的兴趣蓬勃发展。这些材料是独一无二的，有几个原因。首先，强自旋轨道耦合与磁场、晶体场、多体库仑和其他相互作用竞争，从而驱动新的物理行为，例如在某些铱酸盐中出现的有效自旋1/2状态。其次，与5d轨道尺寸较大相关的键相互作用促进了成对、链状和其他复杂有序的相互作用二聚化。第三，轨道能量的相对论性位移，结合自旋轨道耦合和带宽效应，可以驱动能带反转，导致拓扑相位和增强的Rashba分裂。在3d/5d杂化材料中，这些特性与强磁矩和3d离子相关效应的相互作用提供了更大的化学灵活性和功能丰富性。本项目的目标是提高对自旋轨道耦合如何增强含有3d和5d离子的化合物的功能的理解，并阐明特性如何依赖于自旋轨道强度、d壳填充、维度和结构畸变等控制参数。具体来说，该活动包括对多组分硫族化物和氧化物晶体和薄膜中3d和5d过渡金属位点共存的材料进行协调的理论和实验探索。这些材料独特的物理和化学性质为材料发现范式提供了一个平台，其中使用第一性原理计算方法来研究候选材料，确定那些最有希望作为定向合成和深入实验研究目标的材料。目标材料体系包括尚未开发的二元5d碲化物、三元3d-5d碲化物和硒化物、3d-5d硫系超晶格和3d-5d六方链化合物。研究还针对量子异常霍尔、强拓扑绝缘体和Weyl半金属相等拓扑态的新材料和纳米结构的合成进行了研究。研究中使用的方法是多种多样的。利用密度泛函理论和动力学平均场理论等第一性原理方法，通过理论与实验的比较，为重新调整理论和计算工作提供了反馈。该团队提供了体和薄膜（分子束外延和脉冲激光沉积）生长的能力，同时使用x射线、光学、扫描隧道、传输和中子散射技术促进了对独特材料特性的理解和优化。

Non-technical abstractThis research program is focused on understanding and enlarging the class of materials in which atoms from the bottom rows of the periodic table play an important role. Crystalline compounds containing these elements have an interrelated set of properties including strong coupling between electron motion and spin, unusual magnetic behavior, broader electronic energy bands, and a tendency to pairwise attraction of neighboring atoms. Special attention is given to the exploration of layered materials that include tellurium, as these show a wide variety of structural motifs. First-principles computational methods are used to investigate candidate materials of this class, identifying those that appear most promising as targets for directed synthesis and in-depth experimental study. Comparisons between theory and experiment provide feedback to refocus the theoretical and computational effort. The team provides capabilities in bulk and thin-film materials growth coupled to characterization using optical, scattering, and scanning-probe techniques. The activity provides educational opportunities through the involvement of undergraduates in research, the coordination with outreach programs at the Liberty Science Center in New Jersey, and the organization of topical workshops and conferences.Technical AbstractInterest in 5d materials and 3d/5d hybrids has blossomed in recent years in response to scientific advances and applications in the areas of hard magnets, topological insulators, multiferroics, superconductors, and thermoelectrics. These materials are unique for several reasons. First, strong spin-orbit coupling competes with magnetic, crystal-field, many-body Coulomb, and other interactions in such a way as to drive new physical behaviors, such as the effective spin 1/2 state that emerges in certain iridates. Second, the bonding interactions associated with the larger size of the 5d orbitals promotes inter-cation dimerization in pairwise, chain-like, and other complex orderings. Third, the relativistic shifts in orbital energies, combined with spin-orbit coupling and bandwidth effects, can drive band inversions leading to topological phases and enhanced Rashba splittings. In 3d/5d hybrid materials, the interplay of these properties with the strong magnetic moments and correlation effects associate with the3d ions provides greater chemical flexibility and functional richness. The goal of the present project is to improve the understanding of how spin-orbit coupling enhances functionality in compounds containing 3d and 5d ions, and clarify how properties depend on control parameters such as spin-orbit strength, d-shell filling, dimensionality, and structural distortions. Specifically, the activity consists of a concerted theoretical and experimental exploration of materials in which 3d and 5d transition-metal sites coexist in multicomponent chalcogenide and oxide crystals and films. The unique physical and chemical properties of these materials provide a platform for a materials discovery paradigm in which first-principles computational methods are used to investigate candidate materials, identifying those that appear most promising as targets for directed synthesis and in-depth experimental study. Target materials systems include under-explored binary 5d tellurides, ternary 3d-5d tellurides and selenides, 3d-5d chalcogenide superlattices, and 3d-5d hexagonal chain compounds. The research also targets the synthesis of new materials and nanostructures for topological states including quantum anomalous Hall, strong topological insulator, and Weyl semimetal phases.The methods used in the research are diverse. Comparison between theory and experiment provides feedback to refocus the theoretical and computational effort, which is carried out using first-principles methods including density-functional theory and dynamical mean-field theory. The team provides capabilities in both bulk and thin-film (molecular beam epitaxy and pulsed-laser deposition) growth, while the understanding and optimization of the unique materials properties is facilitated using X-ray, optical, scanning tunneling, transport, and neutron scattering techniques.