Large electron–phonon interactions from FeSe phonons in a monolayer

We show that electron–phonon coupling can induce strong electron pairing in an FeSe monolayer on a SrTiO₃ substrate (experimental indications for superconducting $T_c$ are between 65 and 109 K). The role of the SrTiO₃ substrate in increasing the coupling is two-fold. First, the interaction of the FeSe and TiO₂ terminated face of SrTiO₃ prevents the FeSe monolayer from undergoing a shear-type (orthorhombic, nematic) structural phase transition. Second, the substrate allows an anti-ferromagnetic ground state of FeSe which opens electron–phonon coupling channels within the monolayer that are prevented by symmetry in the non-magnetic phase. The spectral function for the electron–phonon coupling (${\alpha }^{2}F$) in our calculations agrees well with inelastic tunneling data. (paper)