Hybridization and suppression of superconductivity inCeFeAsO1−y: Pressure and temperature dependence of the electronic structure

Abstract

Pressure and temperature dependence of the electronic structure of superconducting (SC) ${\text{CeFeAsO}}_{1\ensuremath{-}y}$ and non-SC ${\text{CeFeAsO}}_{1\ensuremath{-}y}$ have been investigated using two complementary hard x-ray spectroscopic probes at the $\text{Ce}\text{ }{L}_{3}$ edge, partial fluorescence yield x-ray absorption spectroscopy and resonant x-ray emission spectroscopy. With increasing pressure, the ratio between the intensity of the peak related to the ${f}^{0}$ $({\text{Ce}}^{4+})$ state and that of the ${f}^{1}$ $({\text{Ce}}^{3+})$ state, $I({f}^{0})/I({f}^{1})$, is found to increase continuously for both compounds, indicating a continuous increase in the Ce valence. The valence of non-SC ${\text{CeFeAsO}}_{1\ensuremath{-}y}$ is found to be slightly higher than that of SC ${\text{CeFeAsO}}_{1\ensuremath{-}y}$ in the entire pressure and temperature ranges of this study. The valence of ${\text{CeFeAsO}}_{1\ensuremath{-}y}$ around 6 GPa, where the superconductivity breaks down, is estimated to be $\ensuremath{\sim}3.0$, but no change in the valence is observed upon cooling. The dependence of the interatomic distances on the concentration of oxygen vacancies is studied via extended absorption fine structure spectroscopy.