Events at Physics
Many of the intriguing electronic properties exhibited by transition metal compounds with partially filled d electron orbitals originate in a competition between many-body states with different spin, orbital and charge ordering patterns. Synchrotron-based resonant x-ray diffraction (RXD) combines the unique ability to directly probe all active degrees of freedom - charge, spin and orbital - with the advantage of being element-specific. It is thus well suited for the investigation of the complex electronic states of d electron systems.
The talk will give an overview of our recent studies on 4d electron ruthenium-based oxides and 5d electron iridium-based sulfides, which were carried out using the RXD technique. In particular, we will discuss the discovery of a new orbital ordering transition between two paramagnetic phases in the layered Mott insulating system Ca2-xSrxRuO4 , the determination of the complex magnetic structure of its bilayered counterpart Ca3Ru2O7 , as well as the determination of the long-discussed magnetic structure of the superconducting magnet RuSr2GdCu2O8 . The results from our ongoing, still unpublished work on the spinel compound CuIr2S4  further demonstrate the power of RXD in unraveling the exciting physics of strongly correlated electron systems.
 I. Zegkinoglou, J. Strempfer, C.S. Nelson, J.P. Hill et al., Phys. Rev. Lett. 95, 136401 (2005)
 B. Bohnenbuck, I. Zegkinoglou, J. Strempfer, C. Schuessler-Langeheine, C.S. Nelson et al., Phys. Rev. B 77, 224412 (2008)
 B. Bohnenbuck, I. Zegkinoglou, J. Strempfer, C.S. Nelson et al., Phys. Rev. Lett. 102, 037205 (2009)
 I.Zegkinoglou, V. Kiryukhin, Ph. Leininger, M.W. Haverkort et al., in preparation