induced by in-situ electron doping*

The potassium dosing is a powerful tool to induce electron doping of surfaces and bulk electronic states that can be directly probed using angle-resolved photoemission spectroscopy. Here, we explore the effect of surface potassium doping of a tetragonal bulk FeSe_1-xS_x superconductor. We find that the system is efficiently doped with electrons and we can follow independently the changes in the band structure and electronic correlations of the electronic states that can be directly probed using angle-resolved photoemission spectroscopy. We identified the opening of the superconducting gap with a high critical temperature and enhanced electronic correlations despite the absence of nematic electronic phases.