paper

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

arXiv:2507.03266 · doi:10.1038/s42005-025-02225-8

Abstract

Kagome metals $A$ V $_{3}$ Sb $_{5}$ ( $A =$ 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/RbV $_{3}$ Sb $_{5}$ versus CsV $_{3}$ Sb $_{5}$ , their influence on the SC order parameter remains unresolved. Here, we investigate low-energy quasiparticle excitations in $A$ V $_{3}$ Sb $_{5}$ , uncovering a striking difference in SC gap anisotropy: K/RbV $_{3}$ Sb $_{5}$ exhibit fully gapped, nearly isotropic $s$ -wave states, in contrast to the strongly anisotropic SC gap in CsV $_{3}$ Sb $_{5}$ . Contrary to previous vortex-state studies suggesting nodal SC in K/RbV $_{3}$ Sb $_{5}$ , our Meissner-state measurements in high-quality crystals demonstrate fully gapped states with reduced anisotropy compared to CsV $_{3}$ Sb $_{5}$ . Impurity scattering introduced via electron irradiation in K/RbV $_{3}$ Sb $_{5}$ has a minimal impact on low-energy excitations, and it induces an increase in the SC transition temperature $T_{c}$ , 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 CsV $_{3}$ Sb $_{5}$ preserves van Hove singularities near the Fermi level, promoting anisotropic $s$ -wave SC with enhanced $T_{c}$ via bond-order fluctuations. These findings establish a systematic framework for understanding the interplay between SC and CDW orders in $A$ V $_{3}$ Sb $_{5}$ , driven by electron correlations.

22 pages, 4 figures