Impact of charge-density-wave pattern on the superconducting gap in Vanadium-based kagome superconductors

Kagome metals AV3Sb5 (A = K, Rb, Cs) provide a compelling platform to explore the interplay between superconductivity (SC) and charge-density-wave (CDW) orders. While distinct CDW orders have been identified in K/RbV3Sb5 versus CsV3Sb5, their influence on the SC order parameter remains unresolved. Here, we investigate low-energy quasiparticle excitations in AV3Sb5, uncovering a striking difference in SC gap anisotropy: K/RbV3Sb5 exhibit fully gapped, nearly isotropic s-wave states, in contrast to the strongly anisotropic SC gap in CsV3Sb5. Impurity scattering introduced via electron irradiation in K/RbV3Sb5 has a minimal impact on low-energy excitations, and it induces an increase in the SC transition temperature Tc, consistent with more isotropic s-wave SC competing with CDW order. Our theoretical analysis attributes the observed SC gap anisotropy differences to distinct CDW modulation patterns: the star-of-David structure unique to CsV3Sb5 preserves van Hove singularities near the Fermi level, promoting anisotropic s-wave SC with enhanced Tc via bond-order fluctuations. These findings establish a systematic framework for understanding the interplay between SC and CDW orders in AV3Sb5, driven by electron correlations. Kagome metal family, AV3Sb5(A = K, Rb, Cs), provide a platform to probe the interplay between superconductivity (SC) and charge density waves (CDW) and whether it is competitive or complementary. Here, the authors find a contrasting behavior that, while the superconductivity in A = Cs is susceptible to disorder, that in A = K, Rb is stabilized by disorder due to the competitive nature between the CDW and SC states. They attribute the results to the different CDW patterns in A = Cs and A = K, Rb, highlighting crucial role of CDW order to the SC order parameters in the kagome family.