Dresden 2009 – wissenschaftliches Programm
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TT: Fachverband Tiefe Temperaturen
TT 19: Correlated Electrons: Metal-Insulator Transition 3
TT 19.2: Vortrag
Dienstag, 24. März 2009, 14:15–14:30, HSZ 301
Spin blockade, orbital occupation and charge ordering in La1.5Sr0.5CoO4 — •Chun Fu Chang1, Zhiwei Hu1, Hua Wu1, Tobias Burnus1, Nils Hollmann1, Mohammed Benomar1, Thomas Lorenz1, Arata Tanaka2, Hong-Ji Lin3, Hui-Huang Hsieh4, Chien-Te Chen3, and Liu Hao Tjeng1 — 1II. Physikalisches Institut, Universität zu Köln, Zülpicher Str. 77, 50937 Köln, Germany — 2Department of Quantum Matter, ADSM, Hiroshima University, Higashi-Hiroshima 739-8530, Japan — 3National Synchrotron Radiation Research Center, 101 Hsin-Ann Road, Hsinchu 30077, Taiwan — 4ChungCheng Institute of Technology, National Defense University, Taoyuan 335, Taiwan
Using Co-L2,3 and O-K x-ray absorption spectroscopy, we reveal that the charge ordering in La1.5Sr0.5CoO4 involves high spin (S=3/2) Co2+ and low spin (S=0) Co3+ ions. This provides evidence for the spin blockade phenomenon as a source for the extremely insulating nature of the La2−xSrxCoO4 series. The associated eg2 and eg0 orbital occupation accounts for the large contrast in the Co-O bond lengths, and in turn, the high charge ordering temperature. Yet, the low magnetic ordering temperature is naturally explained by the presence of the non-magnetic (S=0) Co3+ ions. From the identification of the bands we infer that La1.5Sr0.5CoO4 is a narrow band material.