Distinctive momentum dependent charge-density-wave gap observed in CsV$_3$Sb$_5$ superconductor with topological Kagome lattice

TL;DR

This study reveals a momentum-dependent charge-density-wave gap in CsV$_3$Sb$_5$, showing it is gapped at the $M$ point but gapless near $\Gamma$, providing insights into the coexistence of CDW and superconductivity in this topological Kagome superconductor.

Contribution

The paper provides the first detailed ARPES characterization of the momentum-dependent CDW gap in CsV$_3$Sb$_5$, highlighting its origin from electron scattering between saddle points.

Findings

CDW gap is strongly momentum dependent.

Electronic states are gapless around the $\Gamma$ point.

CDW is driven by electron scattering between $M$ points.

Abstract

CsV$_3$Sb$_5$ is a newly discovered Kagome superconductor that attracts great interest due to its topological nontrivial band structure and the coexistence of superconductivity and charge-density-wave (CDW) with many exotic properties. Here, we report the detailed characterization of the CDW gap in high-quality CsV$_3$Sb$_5$ single crystals using high-resolution angle-resolved photoemission spectroscopy. We find that the CDW gap is strongly momentum dependent. While gapped around the $M$ point, the electronic states remain gapless around the $\Gamma$ point and along the $\Gamma$-$K$ direction. Such momentum dependence indicates that the CDW is driven by the scattering of electrons between neighboring $M$ points, where the band structure hosts multiple saddle points and the density of state diverges near the Fermi level. Our observations of the partially gapped Fermi surface and strongly momentum-dependent CDW gap not only provide a foundation for uncovering the mechanism of CDW in CsV$_3$Sb$_5$, but also shed light on the understanding of how the CDW coexists with superconductivity in this topological Kagome superconductor.