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. Chen⁵ — ¹II. 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 L_2,3 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.