Kagome lattice which consists of a two-dimensional network of corner-sharing triangles provides an excellent platform for exploring new quantum phenomena arising from electronic correlations and non-trivial band topology. Recently, a family of AV3Sb5 (A = K, Rb, Cs) has been discovered to be a novel kagome superconductor with superconducting transition temperature Tc of 0.92-2.5 K [1-3], although kagome metals rarely become superconductors. AV3Sb5 crystallizes in a layered structure consisting of alternating V-kagome lattice layer with hexagonal arrangements of Sb1 atoms, honeycomb-shaped Sb2 layer, and hexagonal A layer [Fig. 1(a)]. In addition to superconductivity, AV3Sb5 undergoes charge-density wave (CDW) transition at TCDW = 78-103 K, and possibly hosts topological surface states. Although this family attracts much attention because of the possible unconventional nature of CDW and its interplay with superconductivity and nontrivial topology, the electronic states relevant to the CDW formation are under intensive debate and the mechanism of CDW and superconductivity is still far from being established.
In this study, we have investigated the electronic structure of AV3Sb5 by photon-energy-tunable angle-resolved photoemission spectroscopy (ARPES) [4,5] and observed multi-orbital nature of the valence band structure in AV3Sb5 [Fig. 1(b)]. Our high-resolution measurements also revealed a drastic electronic reconstruction and an energy gap opening triggered by the CDW transition. We also report the result of detailed band structure mappings above and below TCDW and discuss the mechanism of CDW and its implication to superconductivity through a comparison with the first-principles band-structure calculations.
 B. R. Ortiz et al., Phys. Rev. Mater. 3, 094407 (2019).
 B. R. Ortiz et al., Phys. Rev. Mater. 5, 034801 (2021).
 B. R. Ortiz et al., Phys. Rev. Lett. 125, 247002 (2020).
 K. Nakayama et al., arXiv:2104.08042.
 T. Kato et al., submitted.
Figure: (a) Crystal structure of AV3Sb5. (b) ARPES intensity plots along the ΓKM cut for AV3Sb5 measured with hν = 114 eV at 120 K. The inset shows the first Brillouin zone of AV3Sb5.
Keywords: Kagome lattice, Charge density wave, Superconductivity, Band structure