Abstract

Iron-based unconventional superconductors have attracted intense interest after the critical temperature of FeSe was enhanced by more than one order of magnitude. This was achieved for FeSe placed on top of an insulating oxide substrate with its thickness reduced to the nanometer limit. There are numerous indications of the critical importance of specific features of the FeSe electronic structure in the vicinity of the Fermi surface. Here, we explore how the FeSe band topology changes when located on a Si(001) surface, by first-principles calculations based on the density functional theory. We determine which interface arrangement is preferred and what is the optimal distance between FeSe and Si. Our calculations reveal interesting effects of Si proximity on the FeSe band structure. Bands corresponding to hole pockets at the Γ point in NM FeSe are generally pushed down below the Fermi level. We explain these changes by a redistribution of electrons between different Fe orbitals rather than charge transfer to/from Si.