Berlin 2012 – scientific programme

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TT: Fachverband Tiefe Temperaturen

TT 23: Superconductivity: Fe-based Superconductors - Fe(Se/Te)

TT 23.1: Talk

Wednesday, March 28, 2012, 09:30–09:45, H 2053

Separation of iron spin states in chalcogenide superconductors — Vladimir Gnezdilov¹, •Peter Lemmens², Yurii Pashkevich³, Alexander Gusev³, Tatiana Shevtsova³, Karina Lamonova³, Dirk Wulferding², Ekaterina Pomjakushina⁴, and Kazimierz Conder⁴ — ¹ILTPE NAS, Ukraine — ²IPKM, TU-BS, Braunschweig, Germany — ³DonFTI, Donetsk, Ukraine — ⁴PSI, Villigen, Switzerland

We present a Raman study of superconducting single crystals M_1−xFe_2−ySe₂ (M = Rb, Cs). Our data together with ab-initio spin-polarized band structure and phonon calculations show the presence of two phases: an insulating vacancy ordered Rb₂Fe₄Se₅ phase and a metallic phase with iron in a low spin state. At high frequencies we observe electronic d-d interband transitions, indicating the insulating state. Our results show that iron is in close proximity to a spin state instability. Work supported by DFG and Rus-Ukr.