Feng Ya, Wang Zhijun, Chen Chaoyu, Shi Youguo, Xie Zhuojin, Yi Hemian, Liang Aiji, He Shaolong, He Junfeng, Peng Yingying, Liu Xu, Liu Yan, Zhao Lin, Liu Guodong, Dong Xiaoli, Zhang Jun, Chen Chuangtian, Xu Zuyan, Dai Xi, Fang Zhong, Zhou X J
Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China.
Technical Institute of Physics and Chemistry, Chinese Academy of Sciences, Beijing 100190, China.
Sci Rep. 2014 Jun 20;4:5385. doi: 10.1038/srep05385.
The Dirac materials, such as graphene and three-dimensional topological insulators, have attracted much attention because they exhibit novel quantum phenomena with their low energy electrons governed by the relativistic Dirac equations. One particular interest is to generate Dirac cone anisotropy so that the electrons can propagate differently from one direction to the other, creating an additional tunability for new properties and applications. While various theoretical approaches have been proposed to make the isotropic Dirac cones of graphene into anisotropic ones, it has not yet been met with success. There are also some theoretical predictions and/or experimental indications of anisotropic Dirac cone in novel topological insulators and AMnBi2 (A = Sr and Ca) but more experimental investigations are needed. Here we report systematic high resolution angle-resolved photoemission measurements that have provided direct evidence on the existence of strongly anisotropic Dirac cones in SrMnBi2 and CaMnBi2. Distinct behaviors of the Dirac cones between SrMnBi2 and CaMnBi2 are also observed. These results have provided important information on the strong anisotropy of the Dirac cones in AMnBi2 system that can be governed by the spin-orbital coupling and the local environment surrounding the Bi square net.
狄拉克材料，如石墨烯和三维拓扑绝缘体，因其低能电子受相对论狄拉克方程支配而展现出新颖的量子现象，备受关注。一个特别令人感兴趣的方面是产生狄拉克锥各向异性，使得电子从一个方向到另一个方向的传播方式不同，从而为新特性和应用创造额外的可调性。虽然已经提出了各种理论方法来将石墨烯的各向同性狄拉克锥转变为各向异性狄拉克锥，但尚未取得成功。在新型拓扑绝缘体和AMnBi2（A = Sr和Ca）中也有一些关于各向异性狄拉克锥的理论预测和/或实验迹象，但还需要更多的实验研究。在此，我们报告了系统的高分辨率角分辨光电子能谱测量，这些测量为SrMnBi2和CaMnBi2中强各向异性狄拉克锥的存在提供了直接证据。还观察到了SrMnBi2和CaMnBi2之间狄拉克锥的不同行为。这些结果为AMnBi2体系中狄拉克锥的强各向异性提供了重要信息，这种各向异性可由自旋轨道耦合和Bi方网周围的局部环境所支配。
