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Regensburg 2004 – scientific programme

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TT: Tiefe Temperaturen

TT 24: Postersitzung III: Korrelierte Elektronen, ”Orbital Physics”

TT 24.45: Poster

Wednesday, March 10, 2004, 14:30–19:00, Poster A

Orbital assisted metal insulator transition in VO2 — •L.H. Tjeng1, T. Koethe1, M.W. Haverkort1, Z. Hu1, A. Tanaka2, S. Streltsov3, M. Korotin3, V. Anisimov3, W. Reichelt4, H.H. Hsieh5, H.-J. Lin5, and C.T. Chen51II. Physikalisches Institut, Universität zu Köln — 2ADSM, Hiroshima University, Japan — 3IMP, Ekaterinburg, Russia — 4Institut für Anorganische Chemie, Dresden — 5NSRRC, Hsinchu, Taiwan

VO2 is a non-magnetic oxide that undergoes a metal-to-insulator transition at 340 Kelvin. Above this temperature, VO2 is metallic and has a rutile (TiO2) structure (R-phase). At low temperatures, it is an insulator with a monoclinic structure (M1-phase), in which V-V pairs are formed.

The long-standing debate about this compound concerns the nature of the metal-to-insulator transition. The issue is whether the non-magnetic insulating state would be regarded as a Peierls-insulator with the character of a band insulator (one-electron picture), or whether it should be viewed as a Mott-insulator (many-body picture).

We have used polarization dependent soft-X-ray absorbtion at the V L2,3 edges to investigate the local electronic structure of VO2, and have found that the V 3d orbital occupation symmetry changes dramatically across the metal-insulator transition. From a comparison with LDA and LDA+U calculations we infer that this phase transition is assisted by the orbital degrees of freedom, i.e. requiring an explanation beyond the classical Peierls mechanism.

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