Tuning the structure-property relationships in intermetallic superconductors and magnetic systems with chemical doping

非技术摘要：本研究的重点是对某些具有体磁性或超导性的金属间化合物的磁性和输运性质进行实验研究。所研究的材料的物理性质与它们的晶体结构和潜在的对称性密切相关。事实上，最近在凝聚态物理方面越来越多的研究表明了理解材料拓扑结构的重要性。高质量单晶的合成是该项目的重要组成部分，并使用化学掺杂来调整材料的物理性质。本研究被整合到一个教育计划中，以加强研究生和本科生在实验室和课堂上的学习。一项富有成效的K-12推广工作针对上大学前的少数民族学生，并利用教授、研究生和物理学教育专业的学生。这项实验研究为研究生和本科生在材料合成、结构表征、物理性质测量、数据采集和分析等领域提供了宝贵的经验和训练。除了合成和表征经验外，本科研究员还学习基本的实验室技能并接受低温物理技术的培训。最后，单晶生长和新材料合成帮助美国在高度竞争的全球材料努力中保持重要的存在。技术摘要：本研究的重点是超导体、杂质带铁磁体和高压下形成的新材料，这些系统的显著物理特征是由它们的结构/性质关系驱动的。化学和结构的无序程度是通过掺杂来控制的，可变化学计量学提供了探测材料相空间的能力。本课课组最近在BiPd的电子结构中发现了Dirac表面态，并在其一个体带中发现了非平凡的pi-Berry相，这为进一步的研究提供了动力。特别地，探讨了降维合成，以及空穴掺杂的影响。其次，在电子掺杂的FeGa3中发现了铁磁量子临界点，这表明保留一种新的结构特征（Fe-Fe二聚体）对长程有序的稳定性很重要。在掺Ru和Mn的FeGa3中观察到有趣的磁基态。除了研究与FeGa3相关的化合物外，PI还关注其他含有硼或碳二聚体的材料。最后，利用高压合成能力在硼化物和碳化物全金属钙钛矿族化合物中寻找新的超导体。从这项研究中获得的实验结果有助于理解一般的强相关电子系统。这项研究为新材料的发现提供了机会，并在单晶生长和物理特性表征的多种技术方面培养了下一代材料科学家。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值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 research focuses on an experimental investigation of the magnetic and transport properties of certain intermetallic compounds that display bulk magnetism or superconductivity. The physical properties of the materials being studied are intimately tied to their crystal structures and underlying symmetries. In fact, the growing body of recent research in condensed matter physics shows the importance in understanding a material’s topology. The synthesis of high quality single crystals is an important component of this project, and chemical doping is used to tune the material’s physical properties. This research is integrated into an educational plan to enhance both graduate and undergraduate learning in the laboratory and classroom. A productive K-12 outreach effort targets pre-college minority students and utilizes professors, graduate students, and education majors in physics. This experimental research provides graduate and undergraduate students with valuable experience and training in the areas of materials synthesis, structural characterization, measurement of physical properties, data acquisition, and analysis. In addition to synthesis and characterization experience, the undergraduate researcher learns basic laboratory skills and receives training in techniques of low-temperature physics. Finally, single crystal growth and the synthesis of new materials help the United States to maintain a significant presence in a highly competitive global materials effort. Technical abstract:This research focuses on superconductors, impurity band ferromagnets, and new materials formed under high pressure, where the salient features of the physics in these systems are driven by their structure/property relationships. The level of chemical and structural disorder is controlled through doping, and variable stoichiometry provides the ability to probe the material’s phase space. The recent discovery by the principle investigator’s research group of a Dirac surface state in the electronic structure of BiPd and the existence of a nontrivial pi-Berry phase in one of its bulk bands provide the motivation for further study. In particular, the synthesis in reduced dimensions, along with the effects of hole doping, is explored. Second, the discovery of a ferromagnetic quantum critical point in electron-doped FeGa3 suggests the preservation of a novel structural feature (Fe-Fe dimers) is important for the stability of long-range order. Interesting magnetic ground states observed in FeGa3 doped with Ru and Mn are thoroughly explored. In addition to studying compounds related to FeGa3, the PI focuses on other materials containing boron or carbon dimers. Finally, high-pressure synthesis capabilities are used to search for new superconductors in the boride and carbide all-metal perovskite family of compounds. The experimental results obtained from this research aid in understanding of strongly correlated electron systems in general. This research offers the opportunity for new materials discovery, as well as trains the next generation of materials scientists in multiple techniques of single crystal growth and physical properties characterization.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.