Enhanced Coupling of Superconductivity and Evolution of the Gap Structure in CsV₃Sb₅ via Ta Doping

In this study, Kagome superconductors, i.e., CsV₃Sb₅ single crystals and its Ta-doped variant, Cs(V_0.86Ta_0.14)₃Sb₅, were studied in detail via specific heat measurements. Results revealed that the charge density wave (CDW) was suppressed and the superconducting transition temperature (T_c) considerably increased from 2.8 to 4.6 K upon Ta doping. The electronic specific heat of CsV₃Sb₅ was fitted with a model comprising an s-wave gap and a highly anisotropic extended s-wave gap, where 2∆/κ_BT_c was smaller than the weak coupling limit of 3.5. Cs(V_0.86Ta_0.14)₃Sb₅ exhibited two isotropic s-wave gaps and yielded a larger gap of 2∆/κ_BT_c = 5.04, indicating a significant enhancement in superconducting coupling. This evolution was attributed to the increased density of states near the Fermi level released by CDW gap suppression. These findings demonstrated that Ta doping enhanced superconducting coupling and variation of gap structure in CsV₃Sb₅.