Regensburg 2004 – scientific programme

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TT: Tiefe Temperaturen

TT 14: FV-internes Symposium ”Orbital Physics”

TT 14.8: Invited Talk

Tuesday, March 9, 2004, 16:50–17:20, H18

Resonant Soft Energy X-ray Diffraction of Charge, Spin and Orbital Ordering — •Peter Hatton — Dept. of Physics, University of Durham, UK

Soft x-ray resonant diffraction is a new technique pioneered by our group. We have published examples of the huge resonant enhancements of charge and magnetic scattering that can be obtained at the L-edges of 3d transition metal oxides as well as the first direct observation of orbital ordering. In this talk we will review the technique of soft x-ray diffraction as well as giving recent examples of results In particular we will report the first resonant soft x-ray scattering observations of orbital ordering from a bulk single crystal. We have studied the low temperature phase of La_1.5Sr_0.5MnO₄ that displays charge, spin and orbital ordering. Previous claims of orbital ordering in such materials have relied on observations at the K edge. These claims have attracted a barrage of controversy from theoretical studies. Instead we have employed resonant soft x-ray scattering at the manganese L_III and L_II edges which provides a direct measurement of the orbital ordering. Energy scans at constant wavevector have been compared to theoretical predictions and show that at all temperatures there are two separate contributions to the observed scattering, direct Goodenough orbital ordering and strong cooperative Jahn-Teller distortions of the Mn³⁺ ions.