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

In this study, Kagome superconductors, i.e., CsV_3Sb_5 single crystals and its Ta-doped variant, Cs(V_0.86Ta_0.14)_3Sb_5, were studied in detail via specific heat measurements. Results revealed that the charge density wave (CDW) was suppressed and the superconducting transition temperature (T_\rm c) considerably increased from 2.8 to 4.6 K upon Ta doping. The electronic specific heat of CsV_3Sb_5 was fitted with a model comprising an s-wave gap and a highly anisotropic extended s-wave gap, where 2\varDelta/k_\rm BT_\rm c was smaller than the weak coupling limit of 3.5. Cs(V_0.86Ta_0.14)_3Sb_5 exhibited two isotropic s-wave gaps and yielded a larger gap of 2\varDelta/k_\rm BT_\rm 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 CsV_3Sb_5.