Observation of flat band, Dirac nodal lines and topological surface states in Kagome superconductor CsTi3Bi5
Jiangang Yang, Xin-Wei 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, Xingjiang Zhou
Abstract
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 CsTi 3 Bi 5 , which is isostructural to the AV 3 Sb 5 (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 CsTi 3 Bi 5 from the measured electronic structures. In addition, around the Brillouin zone centre, $${{\mathbb{Z}}}_{2}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msub><mml:mrow><mml:mi>Z</mml:mi></mml:mrow><mml:mrow><mml:mn>2</mml:mn></mml:mrow></mml:msub></mml:math> nontrivial topological surface states are also observed due to band inversion mediated by strong spin-orbit coupling.