Berlin 2008 – wissenschaftliches Programm
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TT: Fachverband Tiefe Temperaturen
TT 34: Correlated Electrons: Metal-Insulator Transition 2
TT 34.10: Vortrag
Donnerstag, 28. Februar 2008, 16:30–16:45, H 2053
Bulk electronic structure of the layered cobaltate La2−xSrxCoO4 — •A. Hendricks, T.C. Koethe, Z. Hu, N. Hollmann, M. Benomar, M. Cwik, T. Lorenz, and L.H. Tjeng — II. Physikalisches Institut Universität zuKöln
The electronic and magnetic properties of the perovskite system La1−xSrxCoO3 has been investigated for many decades now and still is subject of active research. In the undoped compound LaCoO3, the correlated nature of the cobalt 3+ ions leads to a temperature driven spin state transition from a S=0 low spin (LS) ground state to a higher spin state, the nature of which has been discussed controversially as either S=1 intermediate or S=2 high spin (HS) state. Upon introducing Co2+ by doping with Sr, a metal insulator transition and long range ferromagnetic ordering have been observed. Very recently, the related system La2−xSrxCoO4 has been synthesized in order to investigate properties of Co 2+/3+ ions in a environment, which leads in the case of cuprates and nickelates to interesting charge and spin ordering phenomena. While the magnetism of the cobaltates appears to be dominated by Co2+ ions in HS, exhibiting short range magnetic order at low temperatures, the spin state of the Co3+ is still under debate. Using bulk sensitive soft-x-ray photoelectron spectroscopy, we investigated the valence band electronic structure of La2−xSrxCoO4, 0.3 ≤ x ≤ 0.8, and its temperature dependence. Our results demonstrate a strong Co3+ LS contribution.