Electronic instability of kagome metal CsV₃Sb₅ in the 2×2×2 charge density wave state

Recently discovered kagome metals A V 3 Sb 5 ( A = K, Rb, and Cs) provide an ideal platform to study the correlation among nontrivial band topology, unconventional charge density wave (CDW), and superconductivity. The evolution of electronic structures associated with the change of lattice modulations is crucial for understanding of the CDW mechanism, with the combination of angle-resolved photoemission spectroscopy (ARPES) measurements and density functional theory calculations, we investigate how band dispersions change with the increase of lattice distortions. In particular, we focus on the electronic states around M ¯ point, where the van Hove singularities are expected to play crucial roles in the CDW transition. Previous ARPES studies reported a spectral weight splitting of the van Hove singularity around M ¯ point, which is associated with the 3D lattice modulations. Our studies reveal that this “splitting” can be connected to the two van Hove singularities at k z = 0 and k z = π / c in the normal states. When the electronic system enters into the CDW state, both van Hove singularities move down. Such novel properties are important for understanding of the CDW transition.