Chin. Phys. B, 2022, Vol. 31(3): 037101    DOI: 10.1088/1674-1056/ac3ecd
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# Electronic structure and spin–orbit coupling in ternary transition metal chalcogenides Cu2TlX2 (X = Se, Te)

Na Qin(秦娜)1, Xian Du(杜宪)1, Yangyang Lv(吕洋洋)2, Lu Kang(康璐)1, Zhongxu Yin(尹中旭)1, Jingsong Zhou(周景松)1, Xu Gu(顾旭)1, Qinqin Zhang(张琴琴)1, Runzhe Xu(许润哲)1, Wenxuan Zhao(赵文轩)1, Yidian Li(李义典)1, Shuhua Yao(姚淑华)2, Yanfeng Chen(陈延峰)2, Zhongkai Liu(柳仲楷)3,4, Lexian Yang(杨乐仙)1,5, and Yulin Chen(陈宇林)1,3,4,6,†
1 State Key Laboratory of Low Dimensional Quantum Physics, Department of Physics, Tsinghua University, Beijing 100084, China;
2 National Laboratory of Solid State Microstructures, Department of Materials Science and Engineering, Nanjing University, Nanjing 210093, China;
3 School of Physical Science and Technology, ShanghaiTech University and CAS-Shanghai Science Research Center, Shanghai 201210, China;
4 ShanghaiTech Laboratory for Topological Physics, Shanghai 200031, China;
5 Frontier Science Center for Quantum Information, Beijing 100084, China;
6 Department of Physics, Clarendon Laboratory, University of Oxford, Parks Road, Oxford OX1 3 PU, UK
Abstract  Ternary transition metal chalcogenides provide a rich platform to search and study intriguing electronic properties. Using angle-resolved photoemission spectroscopy and ab initio calculation, we investigate the electronic structure of Cu$_{2}$Tl$X_{2}$ ($X=\text{Se, Te}$), ternary transition metal chalcogenides with quasi-two-dimensional crystal structure. The band dispersions near the Fermi level are mainly contributed by the Te/Se p orbitals. According to our ab-initio calculation, the electronic structure changes from a semiconductor with indirect band gap in Cu$_{2}$TlSe$_{2}$ to a semimetal in Cu$_{2}$TlTe$_{2}$, suggesting a band-gap tunability with the composition of Se and Te. By comparing ARPES experimental data with the calculated results, we identify strong modulation of the band structure by spin-orbit coupling in the compounds. Our results provide a ternary platform to study and engineer the electronic properties of transition metal chalcogenides related to large spin-orbit coupling.
Keywords:  transition metal chalcogenides      spin—orbit coupling      electronic structure      angle-resolved photoemission spectroscopy (ARPES)
Received:  28 August 2021      Revised:  26 October 2021      Accepted manuscript online:  01 December 2021
 PACS: 71.70.Ej (Spin-orbit coupling, Zeeman and Stark splitting, Jahn-Teller effect) 71.20.-b (Electron density of states and band structure of crystalline solids) 71.20.Nr (Semiconductor compounds)
Fund: This study was supported by the National Natural Science Foundation of China (Grant No. 11774190). We thank for access to DLS beamline I05 and NSRL beamline 13U with help from S. W. Jung, C. Cacho, S. T. Cui, and Z. Sun.
Corresponding Authors:  Yulin Chen     E-mail:  yulin.chen@physics.ox.ac.uk