Superconductivity in a single layer alkali-doped FeSe: a weakly coupled two-leg ladder system

TL;DR

This study demonstrates superconductivity in a single-layer potassium-doped FeSe film, modeled as a weakly coupled two-leg ladder system, highlighting local pairing mechanisms independent of Fermi surface topology.

Contribution

It introduces a new single-layer FeSe system as a weakly coupled ladder model and shows superconductivity with a pairing mechanism likely driven by local electron correlations.

Findings

Superconductivity observed in single-layer potassium-doped FeSe.

Superconducting gap similar to multilayer films.

Superconductivity is insensitive to Fermi surface changes.

Abstract

We prepare single layer potassium-doped iron selenide (110) film by molecular beam expitaxy. Such a single layer film can be viewed as a two-dimensional system composed of weakly coupled two-leg iron ladders. Scanning tunneling spectroscopy reveals that superconductivity is developed in this two-leg ladder system. The superconducting gap is similar to that of the multi-layer films. However, the Fermi surface topology given by first-principles calculation is remarkably different from that of the bulk materials. Our results suggest that superconducting pairing is very short-ranged or takes place rather locally in iron-chalcogenides. The superconductivity is most likely driven by electron-electron correlation effect and is insensitive to the change of Fermi surfaces.