Two Distinct Superconducting Pairing States Divided by the Nematic End Point in FeSe_1-xS_x

Nematicity in iron-based superconductors has attracted much attention but its relationship with superconductivity has been elusive. We have performed spectroscopic-imaging scanning tunneling microscopy on FeSe_1-xS_x to concurrently study evolutions of the nematic band structure and the superconducting gap. Sulfur substation systematically suppress nematicity that diminishes above the namatic end point at x=0.17. We have found that anisotropy of the in-plane band structure diminishes with increasing x but there is little change in the band parameters at the namatic end point. Superconducting gap is hardly affected by sulfur substitution in the nematic phase but suddenly shrinks above the nematic end point. This means that there are two distinguished superconducting pairing states in FeSe_1-xS_x depending on the presence or absence of nematicity.