Multiple Energy Scales and Anisotropic Energy Gap in the Charge-Density-Wave Phase of Kagome Superconductor CsV3Sb5

TL;DR

This study uses angle-resolved photoemission spectroscopy to reveal multiple energy scales and anisotropic gaps in CsV3Sb5, shedding light on the electronic states related to its charge-density wave and superconductivity.

Contribution

It uncovers the detailed momentum-dependent energy gaps and the role of spin-orbit coupling in CsV3Sb5, advancing understanding of its CDW and superconducting phases.

Findings

Identified a 70-100 meV energy gap at Dirac points.

Discovered a highly anisotropic CDW gap with maxima around 70 meV.

Observed zero gap at the Gamma-centered electron pocket.

Abstract

Kagome metals AV3Sb5 (A = K, Rb, and Cs) exhibit superconductivity at 0.9-2.5 K and charge-density wave (CDW) at 78-103 K. Key electronic states associated with the CDW and superconductivity remain elusive. Here, we investigate low-energy excitations of CsV3Sb5 by angle-resolved photoemission spectroscopy. We found an energy gap of 70-100 meV at the Dirac-crossing points of linearly dispersive bands, pointing to an importance of spin-orbit coupling. We also found a signature of strongly Fermi-surface and momentum-dependent CDW gap characterized by the larger energy gap of maximally 70 meV for a band forming a saddle point around the M point, the smaller (0-18 meV) gap for a band forming massive Dirac cones, and a zero gap at the Gamma-centered electron pocket. The observed highly anisotropic CDW gap which is enhanced around the M point signifies an importance of scattering channel connecting the saddle points, laying foundation for understanding the nature of CDW and superconductivity in AV3Sb5.