Electronic nematicity that spontaneously breaks the rotational symmetry of the nderlying crystal lattice has been a growing issue in high-temperature uperconductivity of iron pnictides/chalcogenides and cuprates. FeSe1−xSx, in which the nematicity can be tuned by isoelectronic sulfur substitution, offers a fascinating opportunity to clarify the direct relationship between the nematicity and superconductivity. Here, we discover a dramatic change in the superconducting gap structure at the critical concentration of sulfur where the nematicity disappears, i.e., nematic critical point. Our observation provides direct evidence that the orbital-dependent nature of the critical nematic fluctuations has a strong impact on the superconducting pairing interaction.

(Click figure for a larger image.)