Regensburg 2007 – wissenschaftliches Programm
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TT: Fachverband Tiefe Temperaturen
TT 20: Correlated Electrons - Poster Session
TT 20.40: Poster
Mittwoch, 28. März 2007, 14:00–17:45, Poster A
X-ray absorption and photoemission study of spin state and metal-insulator transition inGdBaCo2O5.47 — •Z. Hu1, Hua Wu1, T. Koethe1, M. W. Haverkort1, T. Burnus1, J. Gegner1, C. Zobel1, T. Lorenz1, S. N. Barilo2, H.-J. Lin3, N. B. Brookes4, C. T. Chen3, and L. H. Tjeng1 — 1II. Physikalisches Institut,Universität zu Köln, Zülpicher Straße 77, 50937 Köln — 2Institute of Solid State and SemiconductorsPhysics, National Academy of Sciences, Belarus — 3National Synchrotron RadiationResearch Center, Taiwan — 4European Synchrotron Radiation Facility, France
The fundamental physics of the magnetoresistance materials RBaCo2O5.5 (R = Sm, Eu, Gd, Tb, Dy, Y), particularly the issue of spin-state and metal-insulator transition (MIT), is currently under intense debate. Using valence-band photoemission spectra and x-ray absorption spectra at both the O-K and Co-L2,3 edges, we found that crossing the MIT, the band gap decreases but does not collapse across the MIT. More significantly, our spectroscopic evidence firmly rules out the widely accepted model for the low-temperate phase, namely that the Co3+ ions in the octahedral sites are mainly low spin and in the pyramidal sites intermediate spin. We rather found that the MIT in this system is very similar to the high temperature (600 K) MIT of LaCoO3.