Hamburg 2001 – scientific programme
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TT: Tiefe Temperaturen
TT 17: Korrelierte Elektronensysteme Theorie II
TT 17.2: Talk
Wednesday, March 28, 2001, 16:30–16:45, H
The origin of the nearest-neighbour antiferromagnetic exchange in CuGeO3 — •H. Rosner1, S.-L. Drechsler2, W.E. Pickett1, J. Málek3, H. Eschrig2, R. Neudert2, M.S. Golden2, M. Knupfer2, and J. Fink2 — 1Department of Physics, University of California, Davis, CA-9561, USA — 2Institut für Festkörper- und Werkstofforschung Dresden, P.O. Box 270116, D-01171 Dresden, Germany — 3Institute of Physics of Czech Acad. Science, Prague, Czech Rep.
Since its discovery as the first inorganic spin-Peierls system, CuGeO3 has attracted much interest in the field of low-dimensional physics. In a joined theoretical and experimental study, we propose a quantitative explanation for the antiferromagnetic nearest neighbor exchange J1 in CuGeO3. The apparent violation of the Goodenough-Kanamori-Anderson rules in CuGeO3 was ascribed by Gertsma and Khomskii (Phys. Rev. B 54, 3011 (1996)) to an exchange path including the Ge p orbitals. Based on LDA band structure calculations, polarization dependent single crystal O 1s x-ray absorption spectroscopy data and exact diagonalization studies we explain the antiferromagnetic nature of the exchange by a split of the on-site energies of the two relevant oxygen orbitals at the same site due to the strong crystal field. The split leads to a strong reduction of the hole occupation number for the O orbitals oriented perpendicularly to the chain direction and to a quenching of the ferromagnetic contributions to J1, resulting in a total antiferromagnetic exchange.