Superconductivity in Fe1.05Te:Oxsingle crystals

We report the discovery of superconductivity at $\ensuremath{\sim}9$ K in Fe${}_{1.05}$Te single crystals that have been exposed to air for more than six months. The superconductivity is induced due to the oxygen incorporation and only exists in the surface layer of the samples. Our high-resolution transmission electron microscopy experiments and density functional theory calculations show the oxygen prefers to locate at the interstitial site in the Fe-Te layer. X-ray photoelectron spectra characterize an enhancement of the itinerant character of Fe $3d$ electrons, which may reduce the local moment and hence suppress the long-range antiferromagnetism associated with superexchange interactions. This work suggests the bicollinear antiferromagnetism in Fe${}_{1+y}$Te can be suppressed by oxygen incorporation to induce superconductivity and thus could be considered as the parent phase of the superconductivity.