Electronic nature of charge density wave and electron-phonon coupling in kagome superconductor KV(3)Sb(5)

The Kagome superconductors AV(3)Sb(5) (A = K, Rb, Cs) have received enormous attention due to their nontrivial topological electronic structure, anomalous physical properties and superconductivity. Unconventional charge density wave (CDW) has been detected in AV(3)Sb(5). High-precision electronic structure determination is essential to understand its origin. Here we unveil electronic nature of the CDW phase in our high-resolution angle-resolved photoemission measurements on KV(3)Sb(5). We have observed CDW-induced Fermi surface reconstruction and the associated band folding. The CDW-induced band splitting and the associated gap opening have been revealed at the boundary of the pristine and reconstructed Brillouin zones. The Fermi surface- and momentum-dependent CDW gap is measured and the strongly anisotropic CDW gap is observed for all the V-derived Fermi surface. In particular, we have observed signatures of the electron-phonon coupling in KV(3)Sb(5). These results provide key insights in understanding the nature of the CDW state and its interplay with superconductivity in AV(3)Sb(5) superconductors.