Enhanced superconductivity due to forward scattering in FeSe thin films on SrTiO3substrates

We study the consequences of an electron–phonon (e–ph) interaction that is strongly peaked in the forward scattering ( ) direction in a two-dimensional superconductor using Migdal–Eliashberg theory. We find that strong forward scattering results in an enhanced T c that is linearly proportional to the strength of the dimensionless e–ph coupling constant in the weak coupling limit. This interaction also produces distinct replica bands in the single-particle spectral function, similar to those observed in recent angle-resolved photoemission experiments on FeSe monolayers on SrTiO 3 and BaTiO 3 substrates. By comparing our model to photoemission experiments, we infer an e–ph coupling strength that can provide a significant portion of the observed high T c in these systems.