Nodeless superconductivity in the kagome metal CsV₃Sb₅

The recently discovered kagome metal series AV₃Sb₅ (A=K, Rb, Cs) exhibits topologically nontrivial band structures, chiral charge order and superconductivity, presenting a unique platform for realizing exotic electronic states. The nature of the superconducting state and the corresponding pairing symmetry are key questions that demand experimental clarification. Here, using a technique based on the tunneling diode oscillator, the magnetic penetration depth Δλ(T) of CsV₃Sb₅ was measured down to 0.07 K. A clear exponential behavior in Δλ(T) with marked deviations from a T or T² temperature dependence was observed at low temperatures, indicating an absence of nodal quasiparticles. Temperature dependence of the superfluid density and electronic specific heat can be described by two-gap s-wave superconductivity, consistent with the presence of multiple Fermi surfaces in CsV₃Sb₅. These results evidence nodeless superconductivity in CsV₃Sb₅ under ambient pressure, and constrain the allowed pairing symmetry.