No abstract

The kagome metal CsV3Sb5 features an unusual competition between the charge-density-wave (CDW) order and superconductivity. Evidence for time reversal symmetry breaking (TRSB) inside the CDW phase has been accumulating. Hence, the superconductivity in CsV3Sb5 emerges from a TRSB normal state, potentially resulting in an exotic superconducting state. To reveal the pairing symmetry, we first investigate the effect of nonmagnetic impurity. Our results show that the superconducting critical temperature is insensitive to disorder, pointing to conventional s-wave superconductivity. Moreover, our measurements of the self-field critical current (I c,sf ), which is related to the London penetration depth, also confirm conventional s-wave superconductivity with strong coupling. Finally, we measure I c,sf where the CDW order is removed by pressure and superconductivity emerges from the pristine normal state. Our results show that s-wave gap symmetry is retained, providing strong evidence for the presence of conventional s-wave superconductivity in CsV3Sb5 irrespective of the presence of the TRSB.

Materials with AV3Sb5 (A = K, Rb, Cs) stoichiometry are recently discovered kagome superconductors with the electronic structure featuring a Dirac band, van Hove singularities, and flat bands. These systems undergo anomalous charge-density-wave transitions at TCDW∼80–100 K, resulting in the reconstruction of the Fermi surface from the pristine phase. Although comprehensive investigations of the electronic structure via quantum oscillations (QOs) have been performed on the sister compounds CsV3Sb5 and RbV3Sb5, a detailed QO study of KV3Sb5 is so far absent. Here, we report the Shubnikov–de Haas QO study in KV3Sb5. We resolve a large number of new frequencies with the highest frequency of 2202 T (occupying ∼54% of the Brillouin zone area in the kx–ky plane). The Lifshitz-Kosevich analysis further gives relatively small cyclotron effective masses, and the angular dependence study reveals the two-dimensional nature of the frequencies with a sufficient signal-to-noise ratio. Finally, we compare the QO spectra for all three AV3Sb5 compounds collected under the same conditions, enabling us to point out the similarities and the differences across these systems. Our results fill in the gap of the QO study in KV3Sb5 and provide valuable data to understand the band structure of all three members of AV3Sb5.