Atomic and electronic structures of FeSe monolayer and bilayer thin films on SrTiO3 (001): First-principles study

By using first-principles calculations, we have studied the atomic and electronic structures of FeSe monolayer and bilayer thin films on SrTiO3 (001) with SrO or TiO2 termination. We find that both FeSe monolayer and bilayer on either termination behave like a slightly doped semiconductor with a collinear antiferromagnetic order on Fe ions. FeSe is adhered to the SrTiO3 surface by a dipole-dipole interaction. The Fermi surface is mainly of the contribution of Fe-3d orbitals. The valence band contributed mainly by the O-2p orbitals in the TiO2 layer is located slightly below the Fermi level, which can become conducting upon a small doping of holes. For electron-doped SrTiO3 (001) with TiO2 termination, the Fermi level and the energy bands of the FeSe monolayer shift into the energy band gap of the substrate.