Enhanced superconductivity due to forward scattering in FeSe thin films on SrTiO3 substrates

Abstract

We study the consequences of an electron–phonon (e–ph) interaction that is strongly peaked in the forward scattering ( ${\bf{q}}=0$ ) 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 ${\lambda }_{m}$ 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.

Keywords

• superconductivity
• electron-phonon interactions
• Eliashberg theory
• FeSe thin films