Flat Band and $\mathbb{Z}_2$ Topology of Kagome Metal CsTi$_{3}$Bi$_{5}$
Yuan Wang1†, Yixuan Liu1†, Zhanyang Hao1†, Wenjing Cheng1†, Junze Deng2†, Yuxin Wang2, Yuhao Gu2, Xiao-Ming Ma1, Hongtao Rong1, Fayuan Zhang1, Shu Guo1, Chengcheng Zhang1, Zhicheng Jiang3, Yichen Yang3, Wanling Liu3, Qi Jiang3, Zhengtai Liu3, Mao Ye3, Dawei Shen3, Yi Liu4, Shengtao Cui4, Le Wang1, Cai Liu1, Junhao Lin1, Ying Liu1, Yongqing Cai1*, Jinlong Zhu1, Chaoyu Chen1*, and Jia-Wei Mei1*
1Shenzhen Institute for Quantum Science and Engineering (SIQSE) and Department of Physics, Southern University of Science and Technology (SUSTech), Shenzhen 518055, China 2Beijing National Laboratory for Condensed Matter Physics, and Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China 3State Key Laboratory of Functional Materials for Informatics and Center for Excellence in Superconducting Electronics, Shanghai Institute of Microsystem and Information Technology, Chinese Academy of Sciences, Shanghai 200050, China 4National Synchrotron Radiation Laboratory, University of Science and Technology of China, Hefei 230029, China
Abstract：The simple kagome-lattice band structure possesses Dirac cones, flat band, and saddle point with van Hove singularities in the electronic density of states, facilitating the emergence of various electronic orders. Here we report a titanium-based kagome metal CsTi$_{3}$Bi$_{5}$ where titanium atoms form a kagome network, resembling its isostructural compound CsV$_{3}$Sb$_{5}$. Thermodynamic properties including the magnetization, resistance, and heat capacity reveal the conventional Fermi liquid behavior in the kagome metal CsTi$_{3}$Bi$_{5}$ and no signature of superconducting or charge density wave (CDW) transition anomaly down to 85 mK. Systematic angle-resolved photoemission spectroscopy measurements reveal multiple bands crossing the Fermi level, consistent with the first-principles calculations. The flat band formed by the destructive interference of hopping in the kagome lattice is observed directly. Compared to CsV$_{3}$Sb$_{5}$, the van Hove singularities are pushed far away above the Fermi level in CsTi$_{3}$Bi$_{5}$, in line with the absence of CDW. Furthermore, the first-principles calculations identify the nontrivial $\mathbb{Z}_2$ topological properties for those bands crossing the Fermi level, accompanied by several local band inversions. Our results suppose CsTi$_{3}$Bi$_{5}$ as a complementary platform to explore the superconductivity and nontrivial band topology.
2023, Vol. 40 
