CAREER:Designing Hund's Metals from Transition Metal Sulfides

在固态和材料化学计划的支持下，主要研究者的NSF职业计划专注于开发具有功能性磁性和电子特性的新型材料。 这些结晶固体被称为洪德金属，它们独特的电行为来自于丰富的金属如铁和铜与硫的结合。 此外，这些元素聚集在一起形成晶体的方式在定制其材料特性方面非常重要。 为了制备这些新化合物，PI开发了可供更广泛的国家材料科学家社区使用的新化学方法。 该项目为研究生和本科生提供新固体合成和用先进仪器表征其原子结构和物理性质方面的培训。 学生培训的一部分还包括参加外展活动，在那里他们与马里兰州大学附近的高中生接触。 PI和他的大学生小组通过化学辅导和附近国家实验室的图尔斯导游等活动，指导高中化学学生，这些学生主要是西班牙裔、非洲裔美国人，在科学领域的代表性不足。 技术摘要该研究小组从事假设驱动合成新的硫化物定义为洪德金属。 这些材料由后过渡金属硫化物组成，并具有金属的电子特性，同时通过由Hund最大化自旋规则决定的相互作用来表达局部磁性行为。 这些洪德金属的独特性源于d区元素的d轨道行为，包括铁、钴、镍和铜。 虽然五个d轨道中的一个子集形成了穿过费米能级分裂的电子带，就像绝缘体一样，但其他的形成了巡回带。 这些研究项目专门针对含有某些晶体结构基序的硫化物，包括八核簇或d区元素的二维片。 在这两种情况下，过渡金属总是与硫化物阴离子四面体配位，以使晶体场分裂最小化，因此有利于高自旋构型，这导致洪德金属的所需磁性行为。 研究目标包括通过固态合成和晶体生长实验确认预测的相，然后测量新相的磁化强度，电输运和比热性质。 利用中子衍射和非弹性中子散射测量这些硫化物的结构和动力学。 对于二维层状硫化物，为了形成亚稳相，追求软化学方法，如在液氨中嵌入锂，其易于显示非凡的电子行为，如超导性。

Non-Technical SummaryWith support from the Solid State and Materials Chemistry program, the Principal Investigator's NSF CAREER plan focuses on the development of a new class of materials with functional magnetic and electronic properties. These crystalline solids are termed Hund's metals and their unique electrical behavior arises from the combination of abundant metals such as iron and copper with sulfur. Furthermore, the manner in which these elements come together to form crystals is highly important in tailoring their materials properties. To prepare these new compounds, the PI develops new chemical methods available to the broader, national community of materials scientists. The project provides training for both graduate and undergraduate students in the synthesis of new solids and in characterizing their atomic structure and physical properties with advanced instrumentation. Part of the students' training also includes participation in outreach activities where they engage high school students in the immediate vicinity of the University of Maryland. The PI and his group of university students mentor the high school chemistry students, whom are predominately Hispanic, African American and underrepresented in the sciences, through activities that include chemistry tutoring and guided tours of nearby national laboratories. Technical SummaryThe research group is engaged in hypothesis-driven synthesis of new sulfides defined as Hund's metals. These materials are composed of late transition metal sulfides and possess the electronic properties characteristic of a metal while expressing localized magnetic behavior through interactions dictated by Hund's rule for maximizing spin. The uniqueness of these Hund's metals arises from the d-orbital behavior of the d-block elements including iron, cobalt, nickel, and copper. While one subset of the five d-orbitals form electronic bands that split across the Fermi level, as in an insulator, the others form itinerant bands. The research projects specifically target sulfides that contain certain crystal structure motifs including either octanuclear clusters or two-dimensional sheets of the d-block elements. In both cases, the transition metal is always tetrahedrally coordinated to sulfide anions in order to minimize the crystal field splitting and therefore favor a high spin configuration, which leads to the desired magnetic behavior of the Hund's metals. The research goals include experimentally confirming the predicted phases through solid state synthesis and crystal growth followed by measurements of the new phases' magnetization, electrical transport, and specific heat properties. Neutron diffraction and inelastic neutron scattering are utilized to measure both the structure and dynamics in these sulfides. For the two-dimensional layered sulfides, soft chemical methods such as intercalation of lithium in liquid ammonia are pursued in order to form metastable phases, which are prone to display extraordinary electronic behavior such as superconductivity.