High-temperature superconductivity in FeSe-based materials can be realized via pressure, electron doping, or interfacial engineering, however, the underlying pairing mechanism remains unresolved [1,2]. Owing to their multiband, multiorbital electronic structure and the tunability provided by isoelectronic substitution, FeSe-based systems offer a unique platform for investigating the interplay between nematicity, electronic correlations, and superconductivity [3]. In this talk, I will present the evolution of the electronic structure and the emergence of surface superconductivity induced by in-situ potassium dosing of tetragonal FeSe_1-xS_x. Using angle-resolved photoemission spectroscopy (ARPES), we directly observe the coexistence of surface-confined and bulk electronic states and show that increasing electron doping enhances electronic correlations. Surface doping stabilizes a robust superconducting state and gives rise to a superconducting dome as a function of carrier concentration. These results highlight the importance of electron doping and correlation effects in a compensated tetragonal FeSe-based system and provide new insights into the mechanisms that stabilize superconductivity in iron-based superconductors [4].

[1] R. M. Fernandes et al., Nature 601, 35–44 (2022).

[2] C. H. P. Wen, et al., Nature Comm., 7, 10840 (2016).

[3] A.I. Coldea, Front. Phys. 8:594500 (2021).

[4] K. MacFarquharson et al, in preparation (2026).