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

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 $T_{\mathrm{c}}$, 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 $T_{\mathrm{c}}$ 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

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Cited by in corpus (1)

• Microscopic origin of period-four stripe charge-density-wave in kagome metal CsV${}_3$Sb${}_5$