磁性GdX(X=Sb,Bi)材料中拓扑相的形成机理与条件

Topological insulators materials have insulating bulk state and metallic surface state protected by topological invariant, and vast potential applications on spintronic devices, et. al.. Rare earth monopnictides GdSb and GdBi with (π, π, π) antiferromagnetic spin order include spatially 5d-orbitals from magnetic Gd3+ ion, p-orbitals with strong spin-orbitals couplings from Bi3+/Sb3+ions. They are antiferromagnetic topological insulator candidates resulting from d/p band inversion. Each [111] monolayer of GdBi and GdSb is ferromagnetic, and this monolayer with proper lattice parameter is Chern insulator candidate, which affords an excellent platform for the realization of quantum anomalous Hall effect at finite temperature. With the research experience with ferromagnetic GdN and antiferromagnetic GdBiPt, which are Weyl semimetal and antiferromagnetic topological semimetal, respectively, we will study the mechanism and conditions of topological phase in antiferromagnetic GdBi and GdSb. By the combination of single crystal growth with optical floating zone method, theoretical calculation, and Angle-resolved photoelectron spectroscopy (ARPES), we will study the bulk and surfaces state of termination with different spin alignments. We also will theorietically study the magnetic anisotropy and electronic structure of [111] monolayer of GdSb, GdBi, the electronic structure of one dimensional ribbon, and the lattice effect of different substrate. This work is significant to understand the mechanism and conditions of the topological phase in the simple rare earth monopnictides, and an excellent Chern insulator material is expected through this work.

拓扑绝缘体材料具有绝缘的体态及拓扑保护的金属表面态，在未来低功耗电子器件中有着极其重要的应用前景。稀土（π，π，π）型反铁磁材料GdSb及GdBi中含有磁性离子Gd及强自旋轨道耦合效应的Bi/Sb元素。GdSb,GdBi块体及铁磁的 [111]面单层膜分别为反铁磁拓扑绝缘体及高温量子反常霍尔效应的实现提供了重要的研究体系。在前期稀土磁性拓扑半金属材料GdN及GdBiPt的研究基础上，本项目将研究稀土氮族化合物GdSb及GdBi材料中拓扑绝缘相的形成机理和条件。结合理论计算，单晶制备及角分辨光电子谱测量，将系统研究GdSb和 GdBi材料的块体及表面态电子能带结构。通过理论计算研究铁磁[111]面单层膜的磁的各向异性，电子能带结构及一维带状结构的边缘态电子结构；不同晶格参数衬底对铁磁单层膜电子结构及拓扑性质的影响。本研究将有望开拓一类新的拓扑磁性材料体系。

拓扑半金属是当今凝聚态物理研究领域中的热点。拓扑半金属材料中存在能带交叉点及伴随的拓扑电荷。由于拓扑荷的存在，拓扑半金属具有奇异的电磁及光学响应性质。尤其是具有破缺空间/时间反演对称性的拓扑金属为非线性光学性质的研究提供了新的平台。本项目研究了铁磁材料拓扑半金属态的形成机理及条件，以及非中心对称结构的拓扑半金属材料TaAs和RhSi中的非线性效应。通过理论计算，发现铁磁态有利于GdBi及GdSb中Weyl半金属态的形成。此外铁磁的EuB6中也存在Weyl费米子，但非磁性的LaB6及CaB6拓扑平庸，但Ce掺杂的LaB6具有更低的功函数及工作温度，我们掌握了大尺寸Ce掺杂LaB6单晶的光学悬浮区熔生长技术。通过理论计算，本项目进一步证实了Weyl费米子在太赫兹探测方面具有潜在的应用。非中心对称结构的Weyl半金属在太赫兹波段具有非常强的二阶光学电导率。外尔半金属为太赫兹探测提供了一种新的原理和方案。