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TT: Fachverband Tiefe Temperaturen

TT 10: Poster Session: Superconductivity

TT 10.20: Poster

Monday, March 14, 2011, 14:00–18:00, P4

Structural and magnetic properties of the FeAs-based superconductors — •Navid Qureshi¹, Johanna Brand¹, Yvo Drees¹, Jochen Werner², Sabine Wurmehl², Christian Hess², Rüdiger Klingeler², Bernd Büchner², María Teresa Fernández-Díaz³, Paul Steffens³, and Markus Braden¹ — ¹II. Physikalisches Institut, Universität zu Köln — ²Institut für Festkörper- und Werkstoffforschung, Dresden — ³Institut Laue Langevin, Grenoble

The recently discovered family of oxypnictides superconductors has focused the interest of the scientific community as they represent the first non-copper-oxide based layered superconductors reaching a T_c of 55 K. We have combined high-flux and high-resolution neutron and x-ray powder diffraction experiments to study the magnetic and crystal structure of the REO_1−xF_xFeAs series. For RE=La we may unambiguously determine the magnetic symmetry of the undoped material. Upon cooling through the structural and magnetic transitions, the pure and slightly doped materials exhibit anomalies in bond distances and in bond angles which reflect the general magnetophonon coupling in FeAs compounds. Furthermore, we have performed an inelastic neutron scattering study with polarized neutrons and linear polarization analysis on a BaFe₂As₂ single crystal, which may distinguish between the different directional components of the spin fluctuations. Energy scans at the magnetic zone centers (1 0 l) with l being an odd number reveal clear evidence for an anisotropic spin wave excitation at the magnetic zone centers, where the out-of-plane spin fluctuation component surprisingly sets in at lower energy than the in-plane component.