Electronic and lattice structure of CaFe_1−xCo_xAsF probed by x-ray absorption spectroscopy

Abstract

The local lattice and electronic structures of CaFe 1−x Co x AsF (x=0, 0.15) are investigated by Fe Kedge and As K-edge x-ray-absorption near-edge structure and extended x-ray-absorption fine structure from 10 to 300 K. A redistribution of electron density of state between Fe(Co) and As atoms with decreasing temperature has been found in CaFe 0.85 Co 0.15 AsF, resulting in the increase of local density of state near the Fe site. It is found that the doping of Co introduces large static local lattice disorders of the As-Fe(Co) bonds. When we examine the local lattice structure around the Co dopants, we find the static local disorder is much more serious in the Co-As bonds comparing to that of As-Fe(Co) bonds. These facts suggest that strong electron-lattice interaction coexists with superconductivity in Fe-based superconductors.