Unconventional metals in carrier-tuned spin-orbit Mott materials

非技术摘要：这个项目探索了一类金属特有的迷人而复杂的电子行为，这些行为来自绝缘体，这些绝缘体既有电子之间的强相互作用，也有电子轨道运动与其固有磁矩或自旋之间的强耦合。这些自旋轨道辅助的Mott绝缘体可以通过添加载流子转变为金属，其中预测了许多激发态，如高温超导和量子信息的电子态。在该项目中生长了这些金属的超高纯度晶体，并进行了探索其不寻常金属状态的结构、磁性和电子性质的实验。特别是，研究活动针对的是一系列掺杂的氧化Ir材料，这些材料的母体绝缘态最近被证明坍塌成具有反常电荷和自旋性质的金属。这为评估这些材料在未来潜在的超导和量子信息应用中的可行性建立了所需的知识库。该项目培训研究生先进的晶体生长技术以及国家用户设施的先进散射技术，以满足国家对这两个领域训练有素的人员的需求。此外，该项目还开展了一项多层次的教育和外联工作，旨在促进对STEM学科的多样化参与，特别是在材料科学领域。这是通过本科生的研究机会实现的，目的是吸引和保留材料科学中未被充分代表的人口统计学。技术摘要：该项目通过实验探索了两类出现正则自旋轨道Mott态的Ir氧化物--Ruddlesden-Popper系列的SRN 1IrnO3n 1和稀土系列的焦绿石Al2Ir2O7。探索了这些化合物的主要变体，目的是了解Ruddlesden-Popper iriates中非传统自旋和电荷密度波形成的原因，它们与这些系统中奇怪的金属行为和潜在超导电性的关系，以及磁性和焦绿石iriate的金属-绝缘体转变之间的耦合。所有这些现象对于识别预计将在这些材料中出现的奇异电子态具有相当大的兴趣，例如从高温超导到磁性Weyl半金属态。实验方法包括同步加速器X射线和中子散射测量，整体电子性质(如电荷传输和磁化)测量，以及通过合作者网络执行的互补电子探针。研究中的一个关键使能工具是使用高压浮区晶体生长技术来制造用于研究的超高纯度样品。通过利用这一工具，该项目为发现载流子掺杂的自旋轨道辅助Mott材料中的预测和其他不可预见的非常规电子态创造了新的途径。这一奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

Nontechnical Abstract: This project explores the fascinating and complex electronic behaviors endemic to a class of metals born from insulators with both strong interactions between electrons and strong coupling between the electron's orbital motion and its inherent magnetic moment or spin. These 'spin-orbit assisted Mott insulators' can be turned into metals by adding charge carriers, where many exciting states such as high temperature superconductivity and electronic states for quantum information are predicted. Ultrahigh purity crystals of these metals are grown in the project and experiments exploring the structural, magnetic, and electronic properties of their unusual metallic states performed. In particular, research activities target a series of doped iridium oxide materials whose parent insulating states have recently been shown to collapse into metals with anomalous charge and spin properties. This builds the knowledgebase needed for assessing the viability of these materials for potential future superconducting and quantum information applications. The project trains graduate students in advanced crystal growth techniques as well as in advanced scattering techniques at national user facilities, addressing the national need for trained personnel in both arenas. Additionally, the project executes a multitier education and outreach effort targeted at promoting diverse participation in STEM disciplines and within materials science in particular. This is achieved through undergraduate research opportunities targeted at attracting and retaining underrepresented demographics within materials science.Technical Abstract: This project experimentally explores two classes of iridium oxides where canonical spin-orbit Mott states appear--the Ruddlesden-Popper series of Srn+1IrnO3n+1 and the rare-earth series of pyrochlore Al2Ir2O7. Key variants of these compounds are explored with the goals of understanding the origins of unconventional spin and charge density wave formation in the Ruddlesden-Popper iridates, their relation to strange-metal behavior and potential superconductivity in these systems, and the coupling between magnetism and the metal-insulator transitions of the pyrochlore iridates. All of these phenomena are of considerable interest for identifying exotic electronic states predicted to manifest in these materials, with examples ranging from high-temperature superconductivity to magnetic Weyl semimetal states. Experimental approaches include synchrotron x-ray and neutron scattering measurements, bulk electronic properties (such as charge transport and magnetization) measurements, and complementary electronic probes performed via a network of collaborators. A key enabling tool in the research is the use high-pressure floating zone crystal growth techniques to create ultrahigh purity specimens for study. By leveraging this tool, the project creates new pathways for discovering predicted and other unforeseen unconventional electronic states in carrier-doped spin-orbit assisted Mott materials.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.