Nodeless superconductivity in the kagome metal CsV${}_3$Sb${}_5$

Abstract

The recently discovered kagome metal series $A$V${}_3$Sb${}_5$ ($A$=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 $\hat{I}”\hat{I}»(T)$ of CsV${}_3$Sb${}_5$ was measured down to 0.07 K. A clear exponential behavior in $\hat{I}”\hat{I}»(T)$ with marked deviations from a $T$ or $T^2$ temperature dependence is observed at low temperatures, indicating a deficiency 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 CsV${}_3$Sb${}_5$. These results evidence nodeless superconductivity in CsV${}_3$Sb${}_5$ under ambient pressure, and constrain the allowed pairing symmetry.