Two-dimensional superconductors offer a versatile platform for exploring emergent quantum phases and tailoring superconducting properties. Here, we study the evolution of superconductivity in lightly doped CoₓNbSe₂ using ultra-low-temperature scanning tunneling spectroscopy at 45 mK.

We observe a non-monotonic evolution of the superconducting gap structure as a function of doping. In the low-doping regime, the system exhibits clear signatures of multiband superconductivity with two distinct energy gaps. With increasing cobalt concentration, the system transitions into an effective single-gap regime, suggesting suppression or merging of one pairing channel. At higher doping levels, the multiband character re-emerges, restoring a two-gap superconducting state.

This two-band → one-band → two-band evolution highlights a tunable interplay between competing pairing channels, likely driven by doping-induced modifications of the electronic structure and symmetry. Our findings demonstrate a controlled pathway for engineering superconducting states in layered quantum materials, with potential implications for unconventional and topological superconductivity in quantum technologies.