Local structure response of phase separation and iron-vacancy order in KxFe2−ySe2 superconductor

Abstract

We have studied the local structure of a KxFe2−ySe2 superconductor across the phase separation and iron-vacancy order-disorder temperatures (respectively at ∼520 K and ∼580 K). The combination of Fe K edge and Se K edge extended x-ray absorption fine-structure (EXAFS) measurements reveal the glassy local structure of KxFe2−ySe2, with anomalous behavior of local atomic displacements. We find that the Fe-Se distance remains temperature independent while the Fe-Fe distance suffers a substantial effect of the phase separation. Furthermore, the Fe-Se network shows a reduced disorder in the phase separation regime at lower temperature. The x-ray absorption near-edge structure features follow the local structure anomaly observed by EXAFS and reveal substantially reduced Fe 3d–Se 4p hybridization in the iron-vacancy disordered phase at higher temperature. The results provide further information on the role of nanoscale atomic displacements in the peculiar coexistence of different electronic phases in KxFe2−ySe2 with a filamentary superconducting state embedded in the iron-vacancy ordered magnetic texture.

Source-reported materials — not catalogue approval

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