Optimized superconductivity in the vicinity of a nematic quantum critical point in the kagome superconductor Cs(V1-xTix)3Sb5

CsV3Sb5 exhibits superconductivity at T-c = 3.2 K after undergoing intriguing two high-temperature transitions: charge density wave order at similar to 98 K and electronic nematic order at T-nem similar to 35 K. Here, we investigate nematic susceptibility in single crystals of Cs(V1-xTix)(3)Sb-5 (x = 0.00-0.06) where double-dome-shaped superconducting phase diagram is realized. The nematic susceptibility typically exhibits the Curie-Weiss behaviour above T-nem, which is monotonically decreased with x. Moreover, the Curie-Weiss temperature is systematically suppressed from similar to 30 K for x = 0 to similar to 4 K for x = 0.0075, resulting in a sign change at x = similar to 0.009. Furthermore, the Curie constant reaches a maximum at x = 0.01, suggesting drastically enhanced nematic susceptibility near a putative nematic quantum critical point (NQCP) at x = similar to 0.009. Strikingly, T-c is enhanced up to similar to 4.1 K with full Meissner shielding realized at x = similar to 0.0075-0.01, forming the first superconducting dome near the NQCP. Our findings directly point to a vital role of nematic fluctuations in enhancing the superconducting properties of Cs(V1-xTix)(3)Sb-5.