Effect of the Additional Se Layer on the Electronic Structure of Iron-Based Superconductor FeSe/SrTiO3

We use density functional theory to study the structure and the band structure of the monolayer FeSe deposited on the SrTiO3 substrate with the additional layer of Se between them. The top of the SrTiO3 is formed by the double TiOx layer with and without oxygen vacancies. Several structures with different arrangements of the additional Se atoms above the double TiOx layer are considered. Equilibrium structures were found, and the band structures for them were obtained. Near the Gamma = (0,0,0) point of the Brillouin zone, the hole Fermi surface pockets persist and, additionally, an electron pocket appears. Thus, neither the presence of the additional Se layer nor the oxygen vacancies in the double TiOx layer lead to the sinking of hole bands below the Fermi level near the Gamma point. The necessity to include the strong electronic correlations into account is discussed.