Impact of Valence States on Superconductivity of Oxygen Incorporated Iron Telluride and Iron Selenide Films

TL;DR

This study investigates how oxygen incorporation alters the electronic structure and valence states of FeTe and FeSe films, revealing contrasting effects on their superconductivity, with FeTe becoming superconducting and FeSe losing superconductivity.

Contribution

It provides new insights into the role of valence state changes and chalcogenide responses in modulating superconductivity in oxygen-incorporated FeTe and FeSe films.

Findings

Oxygen incorporation induces Fe3+ state in both films.

Te and Se exhibit different valence responses to oxidation.

Superconductivity is enhanced in FeTe but suppressed in FeSe after oxygen incorporation.

Abstract

We report on the local electronic structure of oxygen incorporated FeTe and FeSe films and how this relates to superconductivity observed in these films. In the case of FeTe, intially grown films are measured to be non-superconducting, but become superconducting following oxygen incorporation. In FeSe the opposite happens, initially grown films are measured to be superconducting, but experience a quenching of superconductivity following oxygen incorporation. Total Fluorescence Yield (TFY) X-ray absorption experiments show that oxygen incorporation changes the initial Fe valence state in both the initially grown FeTe and FeSe films to mainly Fe3+ in the oxygen incorporated films. In contrast we observe that while Te moves to a mixed Te0/Te4+ valence state, the Se always remains Se0. This work highlights how different responses of the electronic structure by the respective chalcogenides to oxidation could be related to the mechanisms which are inducing superconductivity in FeTe and quenching superconductivity in FeSe.