Observation of Double-Dome Superconductivity in Potassium-Doped FeSe Thin Films

TL;DR

This study discovers two distinct superconducting phases in potassium-doped FeSe thin films, revealing different sensitivities to doping and disorder, and providing insights into the mechanisms of superconductivity in FeSe-based materials.

Contribution

It reports the first observation of double-dome superconductivity in K-doped FeSe films, highlighting the different pairing mechanisms in each dome and the role of doping and layer thickness.

Findings

Two disconnected superconducting domes observed in K-doped FeSe.

Higher-Tc dome shows robustness against disorder and uniformity.

Superconducting gap of ~14 meV in heavily doped films.

Abstract

We report on the emergence of two disconnected superconducting domes in alkali-metal potassium (K)-doped FeSe ultra-thin films grown on graphitized SiC(0001). The superconductivity exhibits hypersensitivity to K dosage in the lower-Tc dome, whereas in the heavily electron-doped higher-Tc dome it becomes spatially homogeneous and robust against disorder, supportive of a conventional Cooper-pairing mechanism. Furthermore, the heavily K-doped multilayer FeSe films all reveal a large superconducting gap of ~ 14 meV, irrespective of film thickness, verifying the higher-Tc superconductivity only in the topmost FeSe layer. The unusual finding of a double-dome superconducting phase has stepped towards the mechanistic understanding of superconductivity in FeSe-derived superconductors.