Tailoring bulk anisotropic gap in Kagome superconductor through particle irradiation

To investigate the unusual competition between superconductivity and the charge density wave (CDW) state observed in the Kagome lattice compounds AV₃Sb₅ (A = K, Rb, Cs), we have explored the effect of disorder induced by proton irradiation in high-quality single crystalline CsV₃Sb₅. Using multiple complementary techniques, we present the full superconducting phase diagram in pristine and irradiated samples and find behavior consistent with multiple-gap superconductivity. A positive H_c2(T) curvature, common to multigap superconductors, disappears with increasing disorder, consistent with increased scattering rendering the multiple gaps equivalent. Both T_c and T_CDW are suppressed with increasing disorder. While the superconducting transition unexpectedly sharpens with increasing disorder, the CDW transition vanishes once T_c is suppressed to one half of its original value. Furthermore, the effects of irradiation-induced disorder are reversible upon thermal annealing suggesting that the created defects are point defects rather than cascades. Specifically, (1) both T_c and T_CDW recover, (2) the superconducting transition width broadens to its original value, and (3) the positive curvature in H_c2(T) returns, indicating recovery of the multigap state. These findings are unexpected in a scenario where the superconducting and CDW states compete for the same electrons at the Fermi surface.