新型三维Dirac材料中量子输运行为与超导电性研究

After the discovery of a lot of exotic quantum behavior and the prospect of many attractive applications of the topological insulators and graphene with the Dirac cone in their electronic structure, it becomes one of the most important subject in the condensed matter physics to search for new 3D materials with a similar electronic structure. In this project, (1) Several types of this kind materials will be obtained by the synthesis for new compounds and the calculation for their electronic structure. (2) For the 3D materials, such as half Heusler compounds, Tl-based ternary chalcogenides, and (Sr,Ca)MnBi2 layer compounds, with a similar electronic structure which has been predicted by the theoretical calculation, some have been confirmed by the ARPES experiments, their carrier concentration will be modified by means of chemical doping or applying electric field. We expect to get new superconductors, then characterize their superconductivity.(3) For some compounds with both the traditional magnetic order and the Dirac fermions, their transport properties, such as Hall effect, magneto-resistance, thermoelectricity et al., will be measured to search for new quantum states. (4) For the (Tl,K,Rb)0.8Fe1.6Se2 compounds discovered recently by us, which have a super-lattice of Fe vacancies on the iron-plane, and should be a topological insulator predicted by a theoretical calculation, we shall re-check their electronic structure by ARPES experiment after obtaining high quality single crystals to confirm the existence of Dirac cone in its surface state. It will be studied that the relationship between its topological insulator behavior and Fe-based superconductivity emerging in this system. These results will provide more choices for the studies on the Dirac fermions condensed matter physics.

基于具有Dirac锥电子结构的拓扑绝缘体、石墨烯材料所呈现的诸多奇异量子行为和诱人的应用前景，寻找类似新型三维材料已成为凝聚态物理学科重要研究方向之一。本课题将通过新型化合物合成，结合电子能带计算，寻找到几类这种材料；针对理论预言、部分被实验证实，具有同样电子结构的半Heusler型化合物、Tl基硫族化合物和(Sr,Ca)MnBi2层状化合物等三维材料，采用化学替代或外加电场手段，调节其载流子浓度和结构，以期获得新型超导体，并对其超导电性进行表征；在一些磁有序与拓扑绝缘态共存化合物中，通过对其Hall效应、磁阻各向异性、热电效应等输运性质的观测，揭示其量子行为；针对我们最近发现的具有Fe空位超格子结构(Tl,K,Rb)0.8Fe1.6Se2化合物，对其电子结构进行进一步观测，试图证实其拓扑绝缘体行为、及与该系统超导电性的关联。这些研究结果将为Dirac费米子凝聚态物理研究提供更多选项。

基于具有Dirac锥电子结构的拓扑绝缘体、石墨烯材料所呈现的诸多奇异量子行为和诱人的应用前景，寻找新型具有类似电子结构的三维材料已成为凝聚态物理学科重要研究方向之一。在该基金的资助下，基于新型三维Dirac拓扑材料及其新的量子态(包括超导电性），我们开展了多方面研究工作。首先我们发现了一大类新型Ni基超导体: TlNi2Se2-xSx和CsNi2Se2，与国际上一流研究组合作，利用我们制备的单晶，就其超导电性、电子结构、元素替代效应和压力效应做出了一大批工作，相继在PRB上发表论文5篇，大大丰富对Ni基超导体的认识。基于能带理论计算对Weyl半金属预言，我们组在国际上率先生长出TaP单晶，对其磁阻、Hall系数等物性的测量，发现了负磁阻效应，证实了理论计算的正确性，该项工作发表在Sci. China- Phys. Mech. Astron. 后，入选全球高引论文清单。我们在成功生长出BaMnBi2单晶的基础上，在证实该类化合物为Dirac材料的同时，通过外加压强调控，在这类含有Mn原子的层状反铁磁化合物中首次观察了超导电性，该项工作发表在Scientific Report上。另外我们还就磁量子临界行为、Fe基化合物中Mott绝缘体相变以及压力效应、非中心对称超导电性、新型Co氧化物和磁热材料探索等开展了系列研究。以我们为主或与他人合作在国际一流学术刊物发表论文19篇，其中PRL1篇(Editor’s Suggestion)，PRB 7篇，Scientific Reports 2篇，JOP 1篇，J. of Crystal Growth 1篇，Sci. China- Phys. Mech. Astron. 1 篇（入选全球高引论文清单），培养博士生7名，硕士研究生10名，圆满完成项目预定研究计划。

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