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 F-2) in our calculations agrees well with inelastic tunneling data.