Interface enhanced electron-phonon coupling and high temperature superconductivity in potassium-coated ultra-thin FeSe films on SrTiO3

TL;DR

This study demonstrates that potassium coating on ultra-thin FeSe films on SrTiO3 enhances electron-phonon coupling at the interface, leading to high-temperature superconductivity with a large superconducting gap.

Contribution

It provides experimental evidence linking interface-enhanced electron-phonon coupling to high-temperature superconductivity in FeSe/SrTiO3 heterostructures.

Findings

Superconducting gap larger than 11 meV observed at optimal potassium coverage.

Distinct phonon modes identified at 11 meV and 21 meV.

Interface electron-phonon coupling is critical for high-temperature superconductivity.

Abstract

Alkali-metal (potassium) adsorption on FeSe thin films with thickness from two unit cells (UC) to 4-UC on SrTiO3 grown by molecular beam epitaxy is investigated with a low-temperature scanning tunneling microscope. At appropriate potassium coverage (0.2-0.3 monolayer), the tunneling spectra of the films all exhibit a superconducting-like gap larger than 11 meV (five times the gap value of bulk FeSe), and two distinct features of characteristic phonon modes at 11 meV and 21 meV. The results reveal the critical role of the interface enhanced electron-phonon coupling for possible high temperature superconductivity in the system and is consistent with recent theories. Our study provides compelling evidence for the conventional pairing mechanism for this type of heterostructure superconducting systems.