Microscopic evidence for anisotropic multigap superconductivity in the CsV3Sb5 kagome superconductor

Abstract

The recently discovered kagome superconductor CsV3Sb5 (Tc ≃ 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 anisotropic superconducting properties of CsV3Sb5 by means of transverse-field muon spin rotation (μSR) experiments. The fits of temperature dependences of in-plane and out-of-plane components of the magnetic penetration depth suggest that the superconducting order parameter may have a two-gap (s + s)-wave symmetry. The multiband nature of superconductivity could be further supported by the different temperature dependences of the anisotropic magnetic penetration depth γλ(T) and upper critical field $${\gamma }_{{{{{\rm{B}}}}}_{{{{\rm{c}}}}2}}(T)$$ γ B c 2 ( T ) . The relaxation rates obtained from zero field μSR experiments do not show noticeable change across the superconducting transition, indicating that superconductivity does not break time reversal symmetry.

Time-reversal symmetry-breaking charge order in a kagome superconductor

“…According to our numerical analysis (see the methods section) our observation of two step behavior of λ(T ) in KV 3 Sb 5 is consistent with two gap superconductivity with very weak interband coupling (0.001-0.005) and strong electron-phonon coupling. The multi gap superconductivity was also recently reported for the sister compound CsV 3 Sb 5 by means of µSR 35 and STM 36 . The multi-gap superconductivity in KV 3 Sb 5 is consistent with the presence of multiple Fermi surfaces revealed by electronic structure calculations and tunneling measurements 14 .…”

“…The not expected observation of slightly smaller penetration depth λc compared to λ ab might therefore originate in a slightly stronger disorder of the vortex lattice when the field is applied within the kagome plane. Another possibility for the similar values of the penetration depths λ ab and λc in KV3Sb5 might be the following: we have recently measured SC anisotropy in the related system CsV3Sb5 35 . The anisotropy of the magnetic penetration depth is found to be around γ λ ≃ 3 which is a factor of 3 smaller than the anisotropy of the second magnetic critical field γHc2 ≃ 9 35 .…”

“…Another possibility for the similar values of the penetration depths λ ab and λc in KV3Sb5 might be the following: we have recently measured SC anisotropy in the related system CsV3Sb5 35 . The anisotropy of the magnetic penetration depth is found to be around γ λ ≃ 3 which is a factor of 3 smaller than the anisotropy of the second magnetic critical field γHc2 ≃ 9 35 . Such a difference was explained in terms of multiband superconductivity in comparison with well established multigap superconductors (MgB2, Fe-based, and etc).…”

Time-reversal symmetry broken by charge order in CsV3Sb5

“…As demonstrated in Ref. [31], the CsV 3 Sb 5 single crystals possess an obviously hexagonal shape, which allows one to easily distinguish the main crystallographic axes (a and c).…”

“…Single crystals of CsV 3 Sb 5 were grown following the procedure described in Ref. [31]. Single crystals with dimensions of 3 × 3 × 1 mm 3 were used.…”