What controls the superconducting dome of electron-doped FeSe?

Superconducting domes are conspicuous features of the phase diagrams of most unconventional and high-temperature superconductors. The superconducting transition temperature (T_c) of FeSe can be dramatically enhanced with electron doping, but unlike all other high-temperature and unconventional superconductors, its full phase diagram and superconducting dome has yet to be fully explored. Here, we employ a combination of molecular beam epitaxy synthesis, alkali surface doping, in-vacuum electrical transport, and angle-resolved photoemission spectroscopy to investigate the entire superconducting dome of electron-doped FeSe, achieving a fully metallic state where superconductivity is suppressed in the heavily overdoped regime. We identify a robust scaling between T_c and the residual resistivity (ρ₀) which holds across the entire superconducting dome, suggesting that the evolution of T_c is heavily influenced by the evolution of the elastic scattering rate in the high-T_c electron-doped phase. This in turn suggests that the superconducting dome in electron-doped FeSe appears to be fundamentally different than that of other unconventional superconductors where doping plays the primary role, and may instead be driven primarily by the sensitivity of the superconductivity to disorder.