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 Ca_2-xSr_xRuO₄ [1], the determination of the complex magnetic structure of its bilayered counterpart Ca₃Ru₂O₇ [2], as well as the determination of the long-discussed magnetic structure of the superconducting magnet RuSr₂GdCu₂O₈ [3]. The results from our ongoing, still unpublished work on the spinel compound CuIr₂S₄ [4] further demonstrate the power of RXD in unraveling the exciting physics of strongly correlated electron systems.

References:

[1] I. Zegkinoglou, J. Strempfer, C.S. Nelson, J.P. Hill et al., Phys. Rev. Lett. 95, 136401 (2005)
[2] B. Bohnenbuck, I. Zegkinoglou, J. Strempfer, C. Schuessler-Langeheine, C.S. Nelson et al., Phys. Rev. B 77, 224412 (2008)
[3] B. Bohnenbuck, I. Zegkinoglou, J. Strempfer, C.S. Nelson et al., Phys. Rev. Lett. 102, 037205 (2009)
[4] I.Zegkinoglou, V. Kiryukhin, Ph. Leininger, M.W. Haverkort et al., in preparation