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

TL;DR

This paper demonstrates that forward-focused electron-phonon interactions significantly enhance superconductivity in FeSe thin films on SrTiO3, explaining high transition temperatures and spectral features observed experimentally.

Contribution

It introduces a model showing how forward scattering electron-phonon interactions boost $T_c$ and produce replica bands, aligning with experimental observations in FeSe monolayers.

Findings

Enhanced $T_c$ proportional to electron-phonon coupling strength.

Reproduction of replica bands seen in ARPES experiments.

Electron-phonon interaction accounts for high $T_c$ in FeSe/SrTiO$_3$.

Abstract

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