Imaging the emergence of unconventional superconductivity in a doped kagome lattice.

The kagome metals AV₃Sb₅ (A = Cs, K, Rb) have emerged as a rich platform to explore the interplay between geometric frustration, strong electronic correlations, and nontrivial band topology. Superconductivity in this family is particularly intriguing, with theoretical proposals ranging from sign-changing s± to chiral d+id pairing symmetries that may break time-reversal symmetry as seen in some μSR and Kerr effect studies . Here, we investigate the doping evolution in RbV₃Sb₅₋ₓSnₓ using spectroscopic-imaging scanning tunnelling microscopy. Close to the optimally doping (x = 0.3), we uncover clear evidence for a two-gap superconducting order parameter, revealed both by distinct spectroscopic features and quasiparticle interference within the larger gap energies. Atomic-scale imaging of the Sb honeycomb layer further identifies two types of defect-induced bound states that are absent in the pristine and lightly doped compounds. By comparing the experimental results with a theoretical model for the impact of magnetic and non-magnetic impurities on different types of pairing state of kagome superconductors, we narrow down the symmetry of the underlying superconducting state of these compounds.