Oxygen adsorption induced superconductivity in ultrathin FeTe film on SrTiO3(001)

TL;DR

This study reveals that oxygen molecules adsorbed on ultrathin FeTe films induce superconductivity through charge transfer, with microscopic evidence showing a superconducting gap and weak interaction between oxygen and FeTe.

Contribution

The paper provides the first microscopic evidence of oxygen-induced superconductivity in FeTe films, highlighting the role of oxygen overlayer and charge transfer in this process.

Findings

Oxygen molecules form a crystalline overlayer on FeTe at low temperature.

Oxygen overlayer causes hole doping, leading to superconductivity.

Superconducting gap of 4.5 meV observed in oxygenated FeTe.

Abstract

The phenomenon of oxygen incorporation induced superconductivity in iron telluride (Fe1+yTe, with antiferromagnetic (AFM) orders) is intriguing and quite different from the case of FeSe. Until now, the microscopic origin of the induced superconductivity and the role of oxygen are far from clear. Here, by combining in-situ scanning tunneling microscopy/spectroscopy (STM/STS) and x-ray photoemission spectroscopy (XPS) on oxygenated FeTe, we found physically adsorbed O2 molecules crystallized into c(2/3x2) structure as an oxygen overlayer at low temperature, which was vital for superconductivity. The O2 overlayer were not epitaxial on the FeTe lattice, which implied weak O2-FeTe interaction but strong molecular interactions. Energy shift observed in the STS and XPS measurements indicated hole doping effect from the O2 overlayer to the FeTe layer, leading to a superconducting gap of 4.5 meV opened across the Fermi level. Our direct microscopic probe clarified the role of oxygen on FeTe and emphasized the importance of charge transfer effect to induce superconductivity in iron-chalcogenide thin films.