  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.
