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Events on Thursday, September 9th, 2010

R. G. Herb Condensed Matter Seminar
Spin, charge and orbital ordering in transition metal compounds: New insights obtained by resonant x-ray diffraction
Time: 10:00 am
Place: 5310 Chamberlin
Speaker: Ioannis Zegkinoglou, Max Planck Institute for Solid State Research, Stuttgart, Germany

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 [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 The results from our ongoing, still unpublished work on the spinel compound CuIr2S4 [4] further demonstrate the power of RXD in unraveling the exciting physics of strongly correlated electron systems.


[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

Host: Franz Himpsel
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Astronomy Colloquium
3-D Dust Radiation Transfer: What can it do for you?
Time: 3:30 pm - 5:00 pm
Place: 4421 Sterling Hall Same Location
Speaker: Barbara Whitney, UW SAL Department
Abstract: I will introduce myself to the department by describing some applications of our radiation transfer codes to the study of star formation on size scales small and large. The codes calculate dust thermal and non-thermal emission, scattering, and polarization in arbitrary 3-D geometries. I will discuss how we can map the structure of the inner disks of T Tauri stars by modeling their optical and infrared variability; our models of Young Stellar Objects (protostars and their circumstellar disks and envelopes) and star forming regions; comparison of a Galactic population synthesis model of YSOs to GLIMPSE catalogs to determine the star formation rate of our Galaxy; determining the star formation rate of the Large Magellanic by counting and modeling YSOs; and galaxy models incorporating stars, YSOs, and interstellar dust, including PAHs. As I dip my toes into the field of extragalactic research, I will be interested to get feedback on whether these codes, which are publicly available, can be useful to you in your research, and what additional development is most desirable (e.g., line emission).
Host: Astronomy Dept
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Graduate Introductory Seminar
Fundamental Interactions, Symmetries, and Neutrinos
Time: 5:30 pm - 6:30 pm
Place: 2223 Chamberlin Hall
Speaker: Balantekin, Heeger, Knutson, Ramsey-Musolf
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