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

TL;DR

This study reveals that CsV$_3$Sb$_5$ exhibits nodeless two-gap s-wave superconductivity, providing insights into its pairing symmetry and electronic structure, which are crucial for understanding its exotic quantum states.

Contribution

The paper provides the first experimental evidence of nodeless superconductivity in CsV$_3$Sb$_5$, using magnetic penetration depth measurements to clarify its pairing symmetry.

Findings

Exponential temperature dependence of penetration depth indicating nodeless gaps

Superfluid density consistent with two-gap s-wave superconductivity

Supports the presence of multiple Fermi surfaces in 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 $\Delta\lambda(T)$ of CsV$_3$Sb$_5$ was measured down to 0.07 K. A clear exponential behavior in $\Delta\lambda(T)$ 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.