Universal Substrate Effect on the Superconductivity of FeSe Monolayer Films

TL;DR

This study investigates the factors influencing high-temperature superconductivity in monolayer FeSe films, demonstrating that interfacial electron-phonon coupling, rather than strain or dielectric effects, plays a key role in enhancing $T_c$.

Contribution

It provides evidence that interfacial electron-phonon coupling is crucial for high $T_c$ in monolayer FeSe, challenging previous assumptions about strain and dielectric effects.

Findings

Superconductivity with $T_c$ of 63 K observed on TiO$_2$ substrate.

Strain and dielectric constant are not primary factors in $T_c$ enhancement.

Electron-phonon coupling at the interface is essential for high $T_c$.

Abstract

To elucidate the mechanisms behind the enhanced $T_c$ in monolayer (1ML) FeSe on SrTiO$_3$ (STO), we grew highly strained 1ML FeSe on the rectangular (100) face of rutile TiO$_2$, and observed the coexistence of replica bands and superconductivity with a $T_c$ of 63 K. From the similar $T_c$ between this system and 1ML FeSe on STO (001), we conclude that strain and dielectric constant are likely unimportant to the enhanced $T_c$ in these systems. A systematic comparison of 1ML FeSe on TiO$_2$ with other systems in the FeSe family shows that while charge transfer alone can enhance $T_c$, it is only with the addition of interfacial electron-phonon coupling that $T_c$ can be increased to the level seen in 1ML FeSe on STO.