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We study the crystalline and electronic properties of the $textrm{Fe}_{1-x}textrm{Co}_xtextrm{Se}$ system ($x=0$, 0.25, 0.5, 0.75, and 1.0) using X-ray diffraction, X-ray spectroscopy and density functional theory. We show that the introduction of Co $3d$ states in FeSe relaxes the bond strengths and induces a structural transition from tetragonal to hexagonal whose crossover takes place at $xapprox0.38$. This structural transition in turn modifies the magnetic order which can be related to the spin state. Using resonant inelastic X-ray spectroscopy we estimate the spin state of the system; FeSe is found to be in a high spin state (S=2), but Fe is reduced to a low spin state upon Co substitution of $x le 0.25$, well below the structural transition. Finally, we show evidence that FeSe is a moderately correlated system but the introduction of Co into the host lattice weakens the correlation strength for $xge0.25$. These novel findings are important to unravel the mechanisms responsible for the superconducting state in iron-chalcogenide superconductors.
We study the electronic properties of the $textrm{Fe}textrm{Se}_{1-x}textrm{Te}_x$ system ($x=0$, 0.25, 0.5, 0.75, and 1) from the perspective of X-ray spectroscopy and density functional theory (DFT). The analysis performed on the density of states
The electronic structure of the vacancy-ordered K$_{0.5}$Fe$_{1.75}$Se$_2$ iron-selenide compound (278 phase) is studied using the first-principles density functional method. The ground state of the 278 phase is stripe-like antiferromagnetic, and its
The Fe K X-ray absorption near edge structure (XANES) of BaFe2-xCoxAs2 superconductors was investigated. No appreciable alteration in shape or energy position of this edge was observed with Co substitution. This result provides experimental support t
The substitutional dependence of valence and spin-state configurations of Sr(Fe$_{1-x}$Co$_x$)$_2$As$_2$ ($x =$ 0, 0.05, 0.11, 0.17, and 0.38) is investigated with near-edge x-ray absorption fine structure at the $L_{2,3}$ edges of Fe, Co, and As. Th
The idea of employing non-Abelian statistics for error-free quantum computing ignited interest in recent reports of topological surface superconductivity and Majorana zero modes (MZMs) in FeTe$_{0.55}$Se$_{0.45}$. An associated puzzle is that the top