Regensburg 2004 – scientific programme

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TT: Tiefe Temperaturen

TT 14: FV-internes Symposium ”Orbital Physics”

TT 14.11: Talk

Tuesday, March 9, 2004, 17:55–18:10, H18

Direct observation of charge order in La_1.8Sr_0.2NiO₄ — •C. Schüßler-Langeheine¹, J. Schlappa¹, Z. Hu¹, M. W. Haverkort¹, M. Benomar¹, O. Friedt¹, E. Schierle², H. Ott², E. Weschke², G. Kaindl², G. A. Sawatsky³, A. Tanaka⁴, M. Braden¹, and L. H. Tjeng¹ — ¹II. Physikalisches Institut, Universität zu Köln — ²Institut für Experimentalphysik, Freie Universität Berlin — ³Department of Physics and Astronomy, University of British Columbia, Vancouver, Canada — ⁴ADSM, Hiroshima University, Japan

We report on the direct observation of charge order in Sr-doped La₂NiO₄ using resonant soft x-ray scattering at the Ni L_2,3 and La M_4,5 resonances. Unlike conventional scattering techniques, which are essentially probing lattice modulations, resonant soft x-ray scattering is very sensitive to the oxidation state and hence particularly suited to study charge-order phenomena. The charge-order superstructure peak from La_1.8Sr_0.2NiO₄ shows a resonant enhancement predominantly at Ni L_2,3 edges, in contrast to the x-ray absorption signal, which is dominated by the La absorption. The details of this energy dependence agree well with charge order in the Ni system, providing a direct experimental observation of this ordered phase. Furthermore, the superstructure peak observed with resonant soft x-ray scattering is much narrower in momentum space than known from conventional scattering techniques, because the comparably short penetration depth of soft x-rays together with the availability of well focused x-ray beams makes this technique sensitive to slight local inhomogeneities of the doping level, which cannot be probed by other techniques.