Observation of flat band, Dirac nodal lines and topological surface states in Kagome superconductor CsTi3Bi5

Jiangang Yang; Xinwei Yi; Zhen Zhao; Yuyang Xie; Taimin Miao; Hailan Luo; Hao Chen; Bo Liang; Wenpei Zhu; Yuhan Ye; Jing-Yang You; Bo Gu; Shenjin Zhang; Fengfeng Zhang; Feng Yang; Zhimin Wang; Qinjun Peng; Hanqing Mao; Guodong Liu; Zuyan Xu; Hui Chen; Haitao Yang; Gang Su; Hongjun Gao; Lin Zhao; X J Zhou

doi:10.1038/s41467-023-39620-0

Observation of flat band, Dirac nodal lines and topological surface states in Kagome superconductor CsTi₃Bi₅

Nat Commun. 2023 Jul 10;14(1):4089. doi: 10.1038/s41467-023-39620-0.

Authors

Jiangang Yang^#^{1

2}, Xinwei Yi^#², Zhen Zhao^#^{1

2}, Yuyang Xie^#^{1

2}, Taimin Miao^{1

2}, Hailan Luo^{1

2}, Hao Chen^{1

2}, Bo Liang^{1

2}, Wenpei Zhu^{1

2}, Yuhan Ye^{1

2}, Jing-Yang You³, Bo Gu^{2

4

5}, Shenjin Zhang⁶, Fengfeng Zhang⁶, Feng Yang⁶, Zhimin Wang⁶, Qinjun Peng⁶, Hanqing Mao^{1

2

7}, Guodong Liu^{1

2

7}, Zuyan Xu⁶, Hui Chen^{1

2

4}, Haitao Yang^{1

2

4}, Gang Su^{8

9

10}, Hongjun Gao^{11

12

13}, Lin Zhao^{14

15

16}, X J Zhou^{17

18

19}

Affiliations

¹ Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing, 100190, China.
² School of Physical Sciences, University of Chinese Academy of Sciences, Beijing, 100049, China.
³ Department of Physics, Faculty of Science, National University of Singapore, Singapore, 117551, Singapore.
⁴ CAS Center for Excellence in Topological Quantum Computation, University of Chinese Academy of Sciences, Beijing, 100190, China.
⁵ Kavli Institute of Theoretical Sciences, University of Chinese Academy of Sciences, Beijing, 100190, China.
⁶ Technical Institute of Physics and Chemistry, Chinese Academy of Sciences, Beijing, 100190, China.
⁷ Songshan Lake Materials Laboratory, Dongguan, Guangdong, 523808, China.
⁸ School of Physical Sciences, University of Chinese Academy of Sciences, Beijing, 100049, China. gsu@ucas.ac.cn.
⁹ CAS Center for Excellence in Topological Quantum Computation, University of Chinese Academy of Sciences, Beijing, 100190, China. gsu@ucas.ac.cn.
¹⁰ Kavli Institute of Theoretical Sciences, University of Chinese Academy of Sciences, Beijing, 100190, China. gsu@ucas.ac.cn.
¹¹ Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing, 100190, China. hjgao@iphy.ac.cn.
¹² School of Physical Sciences, University of Chinese Academy of Sciences, Beijing, 100049, China. hjgao@iphy.ac.cn.
¹³ CAS Center for Excellence in Topological Quantum Computation, University of Chinese Academy of Sciences, Beijing, 100190, China. hjgao@iphy.ac.cn.
¹⁴ Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing, 100190, China. lzhao@iphy.ac.cn.
¹⁵ School of Physical Sciences, University of Chinese Academy of Sciences, Beijing, 100049, China. lzhao@iphy.ac.cn.
¹⁶ Songshan Lake Materials Laboratory, Dongguan, Guangdong, 523808, China. lzhao@iphy.ac.cn.
¹⁷ Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing, 100190, China. XJZhou@iphy.ac.cn.
¹⁸ School of Physical Sciences, University of Chinese Academy of Sciences, Beijing, 100049, China. XJZhou@iphy.ac.cn.
¹⁹ Songshan Lake Materials Laboratory, Dongguan, Guangdong, 523808, China. XJZhou@iphy.ac.cn.

^# Contributed equally.

Abstract

Kagome lattices of various transition metals are versatile platforms for achieving anomalous Hall effects, unconventional charge-density wave orders and quantum spin liquid phenomena due to the strong correlations, spin-orbit coupling and/or magnetic interactions involved in such a lattice. Here, we use laser-based angle-resolved photoemission spectroscopy in combination with density functional theory calculations to investigate the electronic structure of the newly discovered kagome superconductor CsTi₃Bi₅, which is isostructural to the AV₃Sb₅ (A = K, Rb or Cs) kagome superconductor family and possesses a two-dimensional kagome network of titanium. We directly observe a striking flat band derived from the local destructive interference of Bloch wave functions within the kagome lattice. In agreement with calculations, we identify type-II and type-III Dirac nodal lines and their momentum distribution in CsTi₃Bi₅ from the measured electronic structures. In addition, around the Brillouin zone centre, [Formula: see text] nontrivial topological surface states are also observed due to band inversion mediated by strong spin-orbit coupling.