Three-dimensional energy gap and origin of charge-density wave in kagome superconductor KV3Sb5

TL;DR

This study uses angle-resolved photoemission spectroscopy to reveal the three-dimensional energy gap and Fermi surface reconstruction in the charge-density wave state of the kagome superconductor KV3Sb5, providing insights into its microscopic origin.

Contribution

It demonstrates the Fermi surface reconstruction and the nature of the CDW gap in KV3Sb5, linking experimental observations with first-principles calculations to understand the CDW mechanism.

Findings

Fermi surface reconstruction in the CDW state

CDW gap periodicity along the out-of-plane wave vector

Band dispersion matches inverse star-of-David structural distortion

Abstract

Kagome lattices offer a fertile ground to explore exotic quantum phenomena associated with electron correlation and band topology. The recent discovery of superconductivity coexisting with charge-density wave (CDW) in the kagome metals KV3Sb5, RbV3Sb5, and CsV3Sb5 suggests an intriguing entanglement of electronic order and superconductivity. However, the microscopic origin of CDW, a key to understanding the superconducting mechanism and its possible topological nature, remains elusive. Here, we report angle-resolved photoemission spectroscopy of KV3Sb5 and demonstrate a substantial reconstruction of Fermi surface in the CDW state that accompanies the formation of small three-dimensional pockets. The CDW gap exhibits a periodicity of undistorted Brillouin zone along the out-of-plane wave vector, signifying a dominant role of the in-plane inter-saddle-point scattering to the mechanism of CDW. The characteristics of experimental band dispersion can be captured by first-principles calculations with the inverse star-of-David structural distortion. The present result indicates a direct link between the low-energy excitations and CDW, and puts constraints on the microscopic theory of superconductivity in alkali-metal kagome lattices.