Interlayer coupling of magnetism and electronic structure in two-dimensional superconducting systems: fcc Fe on monolayer FeSe

The interplay of magnetism and superconductivity is of long-standing interest in condensed matter physics. Layered and 2D superconductors provide a particular opportunity for studying this due to the fact that layer substitutions and adlayers can be used to combine superconducting and magnetic materials. Here we investigate the coupling between fcc Fe and ${\text{SrTiO}}_{3}$ supported FeSe monolayers. We find that Fe on FeSe monolayers energetically prefers a magnetic fcc structure. The interaction between Fe overlayers and the FeSe monolayer is relatively strong, and in particular it can cause both changes in the FeSe orbital nature near the Fermi level and alterations in the magnetic structure. Notably, we find a change from ${t}_{2g}$ to ${e}_{g}$ orbital character near the Fermi level with Fe overlayers, with the ${e}_{g}$ orbital slightly larger with thick Fe overlayers. We discuss the details of the changes and their origin.