Band structure and charge doping effects of the potassium-adsorbed FeSe/SrTiO3 system

We theoretically study, through combining the density functional theory and an unfolding technique, the electronic band structure and the charge doping effects for the deposition of potassium on multilayer FeSe films grown on SrTiO3 (001) surface. These results form a theoretical baseline for further detailed studies of low-temperature electronic properties and their multiway quantum engineering of FeSe thin films. We explain the Fermi-surface topology observed in experiment and formulate the amount of doped electrons as a function of atomic K coverage. We show that the atomic K deposition efficiently dopes electrons to the top layer of FeSe. Both checkerboard- and pair-checkerboard-antiferromagnetic (AFM) FeSe layers show electron pockets at the M point and no Fermi pocket at the Γ point with moderate atomic K coverage. The electron transfer from the K adsorbate to the FeSe film introduces a strong electric field, which leads to a double-Weyl-cone structure at the M point in the Brillouin zone of checkerboard-AFM FeSe. We demonstrate that with experimentally accessible heavy-electron doping, an electronlike Fermi pocket will emerge at the Γ point, which should manifest itself in modulating the high-temperature superconductivity of FeSe thin films.