Microscopic evidence for anisotropic multigap superconductivity in the CsV${}_3$Sb${}_5$ kagome superconductor

Abstract

The recently discovered kagome superconductor CsV${}_3$Sb${}_5$ ($T_c\simeq 2.5$ K) has been found to host charge order as well as a non-trivial band topology, encompassing multiple Dirac points and probable surface states. Such a complex and phenomenologically rich system is, therefore, an ideal playground for observing unusual electronic phases. Here, we report on microscopic studies of its anisotropic superconducting properties by means of transverse-field muon spin rotation ($\mu$SR) experiments. The temperature dependences of the in-plane and out-of-plane components of the magnetic penetration depth ${\lambda }_{ab}^{-2}(T)$ and ${\lambda }_c^{-2}(T)$ indicate that the superconducting order parameter exhibits a two-gap ($s+s$)-wave symmetry, reflecting the multiple Fermi surfaces of CsV3Sb5. The multiband nature of its superconductivity is further validated by the different temperature dependences of the anisotropic magnetic penetration depth ${\gamma }_{\lambda }(T)$ and upper critical field ${\gamma }_{{\mathrm{B}}_{c2}}(T)$, both in close analogy with the well known two-gap superconductor MgB${}_2$. Remarkably, the high value of the $T_c/{\lambda }^{-2}(0)$ ratio in both field orientations strongly suggests the unconventional nature of superconductivity. The relaxation rates obtained from zero field $\mu$SR experiments do not show noticeable change across the superconducting transition, indicating that superconductivity does not break time reversal symmetry.

9 pages, 4 figures