Observation of an electron band above the Fermi level in FeTe0.55Se0.45 from in-situ surface doping

We used in-situ potassium (K) evaporation to dope the surface of the iron-based superconductor FeTe0.55Se0.45. The systematic study of the bands near the Fermi level confirms that electrons are doped into the system, allowing us to tune the Fermi level of this material and to access otherwise unoccupied electronic states. In particular, we observe an electron band located above the Fermi level before doping that shares similarities with a small three-dimensional pocket observed in the cousin, heavily electron-doped KFe2−xSe2 compound.