סמינר בחומר מעובה: Visualizing Charge Orders and Superconductivity Evolution in the Doped Kagome Series RbV3Sb5-xSnx

The kagome metals AV₃Sb₅ (A = Cs, K, Rb) provide a fertile platform for exploring the interplay between geometric frustration, strong electronic correlations, and nontrivial band topology. Their band structure hosts multiple van Hove singularities (VHSs) that enhance electronic interactions and give rise to a rich set of ordered states, including a charge-density wave (CDW) with broken time-reversal symmetry, loop currents, a pair-density wave (PDW), and superconductivity. We investigate the evolution of electronic states in RbV₃Sb₅₋ₓSnₓ using spectroscopic-imaging scanning tunnelling microscopy. We find that the CDW weakens and eventually collapses with increasing doping, as expected, but notably the PDW disappears at significantly lower doping levels. In the optimally doped sample (x = 0.3)—where the VHS lies closer to the Fermi level and the CDW is fully suppressed—we uncover clear evidence for a two-gap superconducting order parameter, manifested through distinct spectroscopic features. Atomic-scale imaging of the Sb honeycomb layer further reveals defect-induced bound states in the Kagome layer, that are absent in pristine and lightly doped samples. By comparing these observations to theoretical modeling of magnetic and non-magnetic impurity effects for different pairing symmetries in kagome superconductors, we constrain the symmetry of the underlying superconducting state.