Direct Comparison of Magnetic Penetration Depth in Kagome Superconductors AV$_3$Sb$_5$ (A = Cs, K, Rb)

TL;DR

This study measures the magnetic penetration depth in Kagome superconductors AV$_3$Sb$_5$ (A = Cs, K, Rb) revealing fully gapped superconductivity and highlighting differences in superconducting behavior related to their normal-state band structures.

Contribution

It provides the first direct comparison of the superconducting gap structure in AV$_3$Sb$_5$ compounds using scanning SQUID microscopy, showing fully gapped behavior and variations among the compounds.

Findings

All three compounds exhibit fully gapped superconductivity.

KV$_3$Sb$_5$ and RbV$_3$Sb$_5$ have similar temperature dependences of penetration depth.

Differences in superconducting properties correlate with normal-state band structures.

Abstract

We report measurements of the local temperature-dependent penetration depth, $\lambda(T)$, in the Kagome superconductors AV$_3$Sb$_5$ (A = Cs, K, Rb) using scanning superconducting quantum interference device (SQUID) microscopy. Our results suggest that the superconducting order in all three compounds is fully gapped, in contrast to reports of nodal superconductivity in KV$_3$Sb$_5$ and RbV$_3$Sb$_5$. Analysis of the temperature-dependent superfluid density, $\rho_s(T)$, shows deviations from the behavior expected for a single isotropic gap, but the data are well described by models incorporating either a single anisotropic gap or two isotropic gaps. Notably, the temperature dependences of $\lambda(T)$ and $\rho_s(T)$ in KV$_3$Sb$_5$ and RbV$_3$Sb$_5$ are qualitatively more similar to each other than to CsV$_3$Sb$_5$, consistent with the superconducting phase reflecting features of the normal-state band structure. Our findings provide a direct comparison of the superconducting properties across the AV$_3$Sb$_5$ family.