Impact of valence states on the superconductivity of iron telluride and iron selenide films with incorporated oxygen

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 Fe 3+ in the oxygen incorporated films. In contrast we observe that while Te moves to a mixed Te 0 /Te 4+ valence state, the Se always remains Se 0 . 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.

Impact of interstitial oxygen on the electronic and magnetic structure in superconductingFe1+yTeOxthin films

“…Superconductivity is observed in the Fe 1+y TeO x thin-films with T c close to 12K after oxygen incorporation [1][2][3][4][5][6]. Oxygen substitutes Te through the introduction of oxygen during film growth [1,4,6] or occupies an interstitial site by oxygen annealing or by exposing to air after film growth [2][3][4][5][6].…”

“…Oxygen substitutes Te through the introduction of oxygen during film growth [1,4,6] or occupies an interstitial site by oxygen annealing or by exposing to air after film growth [2][3][4][5][6]. The controlled experiment by Zheng et al shows that interstitial oxygen, rather than oxygen substitution, is responsible for the emergence of superconductivity [6].…”

Electronic structure and metal-insulator transition in crystalline magnetic phase-change material Ge1−xFexTe

“…The spin-orbit splitting energy is 13.1 eV. Previously, Fe 2p XPS spectra with approximate shape and spin-orbit splitting energy were observed in compound FeTe [16,17]. This coincidence indicates that Fe occupies cation site to bond with Te in Ge 1Àx Fe x Te films.…”

Impact of thickness on microscopic and macroscopic properties of Fe-Te-Se superconductor thin films

“…In 100nm films, the Te% decreases and correspondingly the Se% increases with the increase of temperature, whereas the ratios Fe/(Te+Se)<1 remain unchanged in favor of superconducting Fe 20 Te is easily to lose with the increase of temperature. In the non-superconducting 30nm samples, both the Fe% and Te% change irregularly by keeping the ratios Fe/(Te+Se)>1.…”