Electronic nature of charge density wave and electron-phonon coupling in kagome superconductor KV3Sb5

TLDR

The Kagome superconductors AV3Sb5 are notable for their nontrivial topological electronic structure, anomalous properties, superconductivity, and an unconventional charge density wave. The study aims to determine the electronic structure of KV3Sb5 with high precision to elucidate the origin of its charge density wave. The authors use high‑resolution angle‑resolved photoemission spectroscopy on KV3Sb5 to uncover the electronic nature of its CDW phase. ARPES reveals CDW‑induced Fermi surface reconstruction, band folding, band splitting, and gap opening at Brillouin zone boundaries; a strongly anisotropic, momentum‑dependent CDW gap is measured on all V‑derived Fermi surfaces, and signatures of electron‑phonon coupling are observed, providing key insights into the CDW state and its interplay with superconductivity.

Abstract

The Kagome superconductors AV3Sb5 (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 AV3Sb5. 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 KV3Sb5. 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 KV3Sb5. These results provide key insights in understanding the nature of the CDW state and its interplay with superconductivity in AV3Sb5 superconductors.