Electronic structure and phase separation of superconducting and nonsuperconducting KxFe2−ySe2 revealed by x-ray photoemission spectroscopy
M. Oiwake, D. Ootsuki, T. Noji, T. Hatakeda, Y. Koike, M. Horio, A. Fujimori, N. L. Saini, T. Mizokawa
DOI 10.1103/PhysRevB.88.224517 · Physical Review B
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Abstract
We have investigated the electronic structure of superconducting (SC) and nonsuperconducting (non-SC) KxFe2−ySe2 using x-ray photoemission spectroscopy (XPS). The spectral shape of the Fe 2p XPS is found to depend on the amount of Fe vacancies. The Fe 2p3/2 peak of the SC and non-SC Fe-rich samples is accompanied by a shoulder structure on the lower binding energy side, which can be attributed to the metallic phase embedded in the Fe2+ insulating phase. The absence of the shoulder structure in the non-SC Fe-poor sample allows us to analyze the Fe 2p spectra using a FeSe4 cluster model. The Fe 3d-Se 4p charge-transfer energy of the Fe2+ insulating phase is found to be ∼2.3 eV which is smaller than the Fe 3d-Fe 3d Coulomb interaction of ∼3.5 eV. This indicates that the Fe2+ insulating state is the charge-transfer type in the Zaanen-Sawatzky-Allen scheme. We also find a substantial change in the valence-band XPS as a function of Fe content and temperature. The metallic state at the Fermi level is seen in the SC and non-SC Fe-rich samples and tends to be enhanced with cooling in the SC sample.
Source-reported materials — not catalogue approval
| Formula | Reported Tc (K) | Pressure (GPa) | Type |
|---|---|---|---|
| KxFe2-ySe2 Archive — visibility unverified Source-occurrence policy only; no material identity or catalogue acceptance is inferred from the formula. | — | Pressure not reported | unknown |
| K0.8Fe1.8Se2 Archive — visibility unverified Source-occurrence policy only; no material identity or catalogue acceptance is inferred from the formula. | — | Pressure not reported | unknown |
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