Abstract Body

The kagome lattice, characterized by its unique geometry and rich electronic band structure, has recently garnered significant interest following the discovery of kagome superconductors AV₃Sb₅ (A = K, Rb, Cs) [1-3]. Despite extensive research efforts, the nature of the superconducting ground state remains elusive, and there is still no consensus on the electron pairing symmetry. Angle-resolved photoemission spectroscopy (ARPES) has proven to be a powerful tool to directly measure the superconducting gap in momentum space, offering valuable insights into the nature of superconductivity. In this presentation, I will share our ultrahigh-resolution and low-temperature ARPES studies on two exemplary CsV₃Sb₅-derived kagome superconductors: Cs(V_0.93Nb_0.07)₃Sb₅, which exhibits charge order, and Cs(V_0.86Ta_0.14)₃Sb₅, which does not show charge order in the normal state [4]. Additionally, I will present our latest findings on the superconducting gap of pristine CsV₃Sb₅ [5]. Furthermore, I will discuss our investigations into electronic kinks in the band structure [6], which suggest the presence of moderate electron-phonon couplings. Finally, the possible pairing mechanisms for these kagome superconductors will be discussed based on these results.

References

[1] T. Neupert et al., Nat. Phys. 18, 137 (2021)

[2] J.X. Yin et al., Nature 612, 647 (2022)

[3] S. D. Wilson & B. R. Ortiz, Nat. Rev. Mater. 9, 420 (2024)

[4] Y. Zhong et al., Nature 617, 488 (2023)

[5] A. Mine et al., arXiv: 2404.18472 (2024)

[6] Y. Zhong et al., Nat. Commun. 14, 1945 (2023)

Acknowledgment

The author thanks Jinjin Liu, Xianxin Wu, Akifumi Mine, J.-X. Yin, Hongxiong Liu, Yongkai Li, Sahand Najafzadeh, Takumi Uchiyama, Takeshi Suzuki, Kecheng Liu, Xinloong Han, Takeshi Kondo, Youguo Shi, Jiangping Hu, Zhiwei Wang, Xun Shi, Yugui Yao, and Kozo Okazaki for their invaluable contributions and fruitful discussions during collaborative works.

Figure 1. (a) Kagome lattice layer in Ta or Nb doped CsV₃Sb₅. (b) Schematic plot of the Fermi surface. The van Hove singularity (VHS) locates at the M point. (c) Phase diagram with Nb and Ta substitution of V atoms and the schematic superconducting gap structure for samples Cs(V_0.93Nb_0.07)₃Sb₅, Cs(V_0.86Ta_0.14)₃Sb₅, and CsV₃Sb₅ revealed by ARPES measurements.

Keywords: Kagome superconductors, Superconducting gap, Electron-phonon coupling, Photoemission spectroscopy