  Recently superconductivity was discovered in the Kagome metal AV3Sb5 (A = K,
Rb, and Cs), which has an ideal Kagome lattice of vanadium. These V-based
superconductors also host charge density wave (CDW) and topological nontrivial
band structure. Here we report the ultralow-temperature thermal conductivity
and high pressure resistance measurements on CsV3Sb5 with Tc = 2.5 K, the
highest among AV3Sb5. A finite residual linear term of thermal conductivity at
zero magnetic field and its rapid increase in fields suggest nodal
superconductivity. By applying pressure, the Tc of CsV3Sb5 increases first,
then decreases to lower than 0.3 K at 11.4 GPa, showing a clear first
superconducting dome peaked around 0.8 GPa. Above 11.4 GPa, superconductivity
re-emerges, suggesting a second superconducting dome. Both nodal
superconductivity and superconducting domes point to unconventional
superconductivity in this V-based superconductor. While our finding of nodal
superconductivity puts a strong constrain on the pairing state of the first
dome, which should be related to the CDW instability, the superconductivity of
the second dome may present another exotic pairing state in this ideal Kagome
lattice of vanadium.
