X-ray spectra and electronic structures of the iron arsenide superconductorsRFeAsO1−xFx(

Abstract

The electronic structures of undoped and fluorine-doped LaFeAsO superconductors and fluorine-doped SmFeAsO superconductors are studied using soft x-ray absorption and emission spectroscopy combined with full potential linearized augmented planes waves ͑FP LAPW͒ calculations. The comparison between the numerical simulations and the experimental Fe L-emission spectra shows that the Fe states are concentrated near E F , suggesting that the materials are not highly correlated systems. The comparison of the O K-edge and F K-edge spectra with the calculated density of states shows that the F dopants do not directly participate in the electronic structure near E F , and so they serve the same purpose as an oxygen vacancy leading to an increase in the number of available charge carriers. Increasing the amount of fluorine doped into the structure of SmFeAsO is shown to cause a narrowing of the bandwidth of occupied O valence states.

Electronic structure of Fe-based superconductors

“…[55] This disagrees qualitatively with experimental data, which show a metallic state, including observation of quantum oscillations, [56,57,58] metallic-like band dispersions around E F , [34,59] and critically the non-observation of Hubbard bands. [60] From this perspective the FeSC behave very differently from cuprate superconductors. At first sight, this may seem surprising as one might wonder how adding the U could degrade results.…”

Band- and momentum-dependent electron dynamics in superconductingBa(Fe1−xCox)<

“…In particular the proximity of the parent antiferromagnetic to the optimal superconducting phase suggests that the copper-oxygen compounds and the iron arsenides may be cousins in the same family. However, the strong metallicity of the parent phase and the lack of spectral redistribution upon doping observed by angle-resolved photoemission (ARPES) and x-ray absorption (XAS) in FeAs argue otherwise 6,7 . But perhaps one of the most telling similarities would be if the iron arsenides had the signature property of all cuprates -an energy gap ∆ k having nodes and a sign change along the Fermi surface 8 .…”

Electronic structure of new oxygen-free 38-K superconductor Ba1−x K x Fe2As2 in comparison with BaFe2As2 from the first principles

“…On the other hand, though the chemical bonding in (La-O) layers is also ionic, the strong covalent interactions inside (FeAs) layers occur. According to the available experimental and theoretical data [13][14][15][16][17][18][19] for LaOFeAs the electronic bands in a window around the Fermi level are formed mainly by states of (Fe-As) layers, whereas the bands of (La-O) layers are rather far from the Fermi level. Thus the superconductivity in LaFeAsO is determined mainly by structural and electronic states of the (Fe-As) layers.…”