Regensburg 2013 – scientific programme

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TT: Fachverband Tiefe Temperaturen

TT 12: Poster Session Superconductivity

TT 12.32: Poster

Monday, March 11, 2013, 15:00–19:00, Poster D

Electronic structure of single-crystalline Sr(Fe_1−xCo_x)₂As₂ probed by x-ray absorption spectroscopy: Evidence for effectively isovalent substitution of Fe²⁺ by Co²⁺ — •Michael Merz¹, Thomas Wolf¹, Peter Nagel¹, Felix Eilers¹, Peter Schweiss¹, Hilbert von Löhneysen^1,2, and Stefan Schuppler¹ — ¹Institut für Festkörperphysik, Karlsruhe Institute of Technology, 76021 Karlsruhe, Germany — ²Physikalisches Institut, Karlsruhe Institute of Technology, 76131 Karlsruhe, Germany

The substitutional dependence of valence and spin-state configurations of Sr(Fe_1−xCo_x)₂As₂ (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. The present data provide direct spectroscopic evidence for an effectively isovalent substitution of Fe²⁺ by Co²⁺, which is in contrast to the widely assumed Co-induced electron-doping effect. Moreover, the data reveal that not only does the Fe valency remain completely unaffected across the entire doping range, but so do the Co and As valencies as well. The data underline a prominent role of the hybridization between (Fe,Co) 3d_xy, d_xz, d_yz orbitals and As 4s/4p states for the band structure in A(Fe_1−xCo_x)₂As₂ and suggest that the covalency of the (Fe,Co)-As bond is a key parameter for the interplay between magnetism and superconductivity.