Dresden 2009 – wissenschaftliches Programm

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TT: Fachverband Tiefe Temperaturen

TT 36: Focussed Session: Superconductivity and Magnetism in Ferropnictides and Related Materials

TT 36.4: Topical Talk

Donnerstag, 26. März 2009, 11:15–11:45, HSZ 03

Relation of structure, magnetism, doping and pressure in AFe₂As₂ — •Helge Rosner, Deepa Kasinathan, Alim Ormeci, Katrin Koch, Miriam Schmitt, Walter Schnelle, Corneliu Miclea, Michael Nicklas, Manoj Kumar, Christoph Geibel, Ulrich Schwarz, and Andreas Leithe-Jasper — MPI CPfS Dresden, Nöthnitzer Str. 40, 01187 Dresden

We present an overview of our recent experimental and theoretical studies on the AFe₂As₂ (A = Sr, Eu, K) compounds. Starting with thermodynamic measurements and band structure results for the undoped SrFe₂As₂ under ambient conditions, we report the influence of hydrostatic pressure and substitution on the A site as well as the Fe site on the magneto-structural and superconducting transitions: (i) SrFe₂As₂ orders antiferromagnetically at 205 K, intrinsically tied to a tetragonal-orthorhombic distortion. (ii) The magnetism is weakened upon application of pressure as indicated by resistivity, X-ray data and calculations. (iii) Similar to substitution on the A site, substitutions on the Fe-site quenches the magnetic transition and induces bulk superconductivity with T_c up to 20 K. (iv) For underdoped SrFe_2−xCo_xAs₂, superconductivity with T_c up to 27 K is observed for pressures of 2.6 GPa. The first observation of bulk superconductivity induced by electron doping in AFe₂As₂ compounds – despite strong disorder in the Fe-As layer – favors an itinerant electronic theory in contrast to the strongly correlated cuprates. Although discrepancies between experiment and calculated electronic structure remain, DFT band structure calculations provide a consistent overall picture of AFe₂As₂ compound.