铼氧化物新材料探索和物性研究

5d transition metal oxides may display physical properties very different from 3d transition metal compounds due to the reduced electronic correlation strength and enhanced spin-orbital coupling (SOC) effect. In 5d oxide materials, the SOC is at a energy scale comparable to the on-site Coulomb repulsion U and the crystal filed splitting energy. Their competition or cooperation will result in exotic properties. So our main focus of this project is to search for new materials on 5d Rhenium (Re) oxide materials: the exploration of novel and high quality new Rhenium oxides; the investigation structure and physical properties of these new materials. The sample preparation is the most important for researching new rhenmium oxide materials in this program. The efforts by applying the atmosphere pressure, high pressure, and high temperature solid state chemical way could be used to search for new materials on rhenium oxide system. Also, assisted by other common ways, such as doping, oxidation-reduction reaction, intercalation reaction, and soft-chemical way, some novel materials can be expected in this sample series. For structural and physical properties characterizations, high sensitive SPring-8, X-ray diffractometer, TEM, Quantum Design MPMS-XL Squid, PPMS, and so on, will serve as an excellent platform.SPring-8 will be used to analyze the crystal structures of the sample. Combined with the TEM and analysis software bundles, we can obtain the detailed structure analysis for the new materials, and find the relationship between the structure and the physical properties. We will characterize the physical properties for new materials by using MPMS and PPMS, including resistivity, magnetic properties, specific heat, thermo-power, Hall coefficient, and so on. In addition, the first-principle calculations on the electronic structures can be used to analyze the physics and verify the experimental data. The 3d and 4d metal oxides have been intensively studied to search for new materials, whereas the 5d Re oxide series are not. However, the previous results for rhenium oxides studies also display ravel complex and multivariate physical phenomena in this system, such as superconductivity, magnetic ordering, etc. These observed novel and unconventional physical properties are the frontier in condensed matter physics. This project is valuable for fundamental research due to the new materials, new phenomena and novel physical properties. These rich properties may generate new insights on the Re oxide system, and help us well understand the 5d metal transitional materials.

本项目将研究金属氧化物铼（Re）体系新材料、结构和奇异物性。从3d-4d-5d,其电子关联效应逐渐减弱，另一方面，自旋轨道耦合却越来越强，它们的竞争或相互作用使得5d过渡金属氧化物可能与3d材料有很大不同。过渡金属铼氧化物已进行的研究同样显示出它们具有复杂和多变的物理行为，包括超导电性、金属-绝缘体相变、磁有序等复杂行为，而这些性质目前是凝聚态物理领域的一个研究热点。我们希望通过铼氧化物新材料的探索，发现新材料、新现象和物性，揭示其背后物理机理。新材料的合成与探索，高品质的单晶生长是研究复杂电子体系竞争序、新奇量子现象与效应的基础。基于我们现有的常规物性测量基础之上，针对具有奇异物性的铼体系新材料，如关联体系中出现的相变、有序态之间的竞争、演生现象等深层次丰富物性，开展更深层次如电子结构和电子态行为、自旋结构和自旋激发等多个方面全面细致物性研究。

本项目原计划研究金属氧化物铼（Re）体系的新材料、结构和奇异物性，但研究过程中未在该方向获得突出进展。但在该基金的支持下，我们在拓扑物态探索、重费米子体系和量子自旋液体材料研究方面得到很多研究成果，并且在功能材料探索中生长出一系列高质量单晶材料，对其物性进行了测试和研究。.主要进展有以下几个方面：（1）在拓扑研究领域，成功首次生长出MoP（磷化钼）单晶样品，并与合作者实验证实突破传统分类的三重简并费米子（Nature 2017）。(2)首次生长了高质量的KHgSb单晶样品，与合作者观测到了非简单空间群拓扑绝缘体KHgSb中的沙漏型费米子(Sci. Adv. 2017)。(3)生长出高质量的TiB2单晶，证明其具有nodal chain的费米面结构，实验与理论计算相符合(PRB 2018)。(4)首次发现了EuMnSb2新材料并成功制备了其单晶样品，发现EuMnSb2低温下处于反铁磁基态，并表现出反常的负磁电阻行为以及反常霍尔电阻行为（PRB2017）。(5)在重费米子体系研究方面，报道了具有准一维链结构的重费米子材料CeCo2Ga8，实验验证其本征的非费米液体行为和量子临界行为（NPJ Quan. 2017）。我们生长得到了高质量的CeCoInGa3单晶，证实其为典型的重费米子材料，并且表现出明显的各向异性的杂化效应(PRB 2018)；在量子自旋液体探索方面，我们首次合成了新的量子自旋液体材料Cu3Zn(OH)6FBr，并在其中发现了自旋1/2的自旋子激发(CPL 2017, PRB 2018)。此外，我们生长了一系列单晶材料，如HgCr2Se4、TaAs2、LaBi、EuCd2As2、Cd3As2、WTe2等，并与合作者仪器研究了其物理性质。