非磁性元素掺杂的拓扑绝缘体Bi2Se3的单晶生长及其磁学性质的研究

The exploration of magnetic topological insulator material has important scientific significance and application value to the basic theory research and the research of new electronic devices with low energy dissipation. However, doping the magnetic elements to obtain the magnetic topological insulator can lead to the problem of non-uniform magnetic elements in the material and occurrence of the second phase or cluster. The theoretical calculations in the early stage of this project found that the C element doping Bi2Se3 can induce magnetic moment and introduce magnetism, and the exploration experiment also confirmed the existence of ferromagnetism.Therefore, this project intends to select non-magnetic elements B, C to dope Bi2Se3 in order to achieve magnetic topological insulators. High-quality single crystals doped with non-magnetic elements will be prepared. And the effects of doping nonmagnetic elements and defects on their band structure and Fermi surface will be study studied. Based on the calculated results, the experimental results and theoretical simulation results will be analyzed to study the magnetic properties after doping as well as the regulation effect of B and C elements on the topological surface states. The essential reason for the stable magnetic properties of Bi2Se3 will be explore.

磁性拓扑绝缘体材料的探索对低能量耗散新型电子器件研究具有重要的科学意义和应用价值。然而磁性元素掺杂获得磁性拓扑绝缘体，会出现第二相、团簇及磁性来源不明确等问题。已有理论发现2p轻元素掺杂Bi2Se3会诱导出磁矩引入磁性，探索实验也证实了铁磁性的存在。因此本项目拟选择非磁性元素B、C对Bi2Se3进行掺杂，以期实现磁性拓扑绝缘体。制备出非磁性元素掺杂单晶，研究掺杂非磁性元素对其磁性、能带结构的影响；结合第一性原理计算，分析实验测试结果，研究B、C元素掺杂对磁学性质及拓扑表面态的调控作用；探究出Bi2Se3产生稳定磁性的本质原因。

项目研究了非磁性元素掺杂的拓扑绝缘体Bi2Se3单晶的生长机理、制备及其磁学性质。系统分析了坩埚下降法Bi2Se3单晶的结晶物理过程；研究了生长速率、界面、饱和蒸汽压与温场的内在关联，优化生长工艺；在两温区单晶炉中，调试出适宜的温场分布，通过籽晶培育和生长，界面控制，生长制备出尺寸Φ20×48mm、径向生长均匀、结晶性能好的优质Bi2Se3单晶体；对生长的晶体进行退火实验，提高晶体质量。研究了Bi2Se3晶体的磁学性能，通过第一性原理研究了能带结构，发现C替代Bi位和Se1位（价带穿过费米能级）都是金属。C替代Se2位：价带顶在Γ点发生分裂，是间接带隙半导体。C插入范德瓦尔斯能隙Gap: 费米能级上移穿过导带，在Γ-K方向，两条价带形成狄拉克锥。采用PPMS和超快光谱分析了单晶薄片样品的宏观输运性质和磁光克尔光谱，测试显示其存在磁性。