# Dipolar phonons and electronic screening in monolayer FeSe on SrTiO$_3$

## TL;DR

This study investigates the interaction between SrTiO$_3$ phonons and electrons in monolayer FeSe, finding that electronic screening weakens the electron-phonon coupling, suggesting it is unlikely to be the main cause of enhanced superconductivity.

## Contribution

The paper provides a systematic analysis of electron-phonon interactions in monolayer FeSe on SrTiO$_3$, highlighting the strong screening effect that diminishes the potential for phonon-mediated superconductivity.

## Key findings

- Electron-phonon interaction is strongly screened by FeSe electronic fluctuations.
- Net electron-phonon coupling is very weak in monolayer FeSe on SrTiO$_3$.
- Screening reduces the likelihood of phonons being responsible for high Tc in this system.

## Abstract

Monolayer films of FeSe grown on SrTiO$_3$ substrates exhibit significantly higher superconducting transition temperatures than those of bulk FeSe. Interaction of electrons in the FeSe layer with dipolar SrTiO$_3$ phonons has been suggested as the cause of the enhanced transition temperature. In this paper we systematically study the coupling of SrTiO$_3$ longitudinal optical phonons to the FeSe electron, including also electron-electron Coulomb interactions at the random phase approximation level. We find that the electron-phonon interaction between FeSe and SrTiO$_3$ substrate is almost entirely screened by the electronic fluctuations in the FeSe monolayer, so that the net electron-phonon interaction is very weak and unlikely to lead to superconductivity.