Dresden 2006 – wissenschaftliches Programm
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TT: Tiefe Temperaturen
TT 31: Correlated Electrons: Metal Insulator Transition - Part 2
TT 31.5: Vortrag
Donnerstag, 30. März 2006, 15:00–15:15, HSZ 301
Evidence for dimer formation in XPS investigation of VO2 — •T.C. Koethe1, Jan Gegner1, Z. Hu1, F. Venturini2, N.B. Brookes2, W. Reichelt3, and L.H. Tjeng1 — 1II. Physikalisches Institut der Universität zu Köln — 2ESRF, Grenoble, France — 3Institut für Anorganische Chemie, TU Dresden
VO2 is a non-magnetic d1-system that undergoes a metal-to-insulator transition (MIT) at 340K. Above this temperature VO2 is metallic and has a rutile 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 MIT. The issue is whether it can be regarded as a Peierls-transition with the character of a band insulator (one electron picture) or whether it should be viewed as a Mott-insulator (many-body-picture). Recently the scenario of an orbital assisted MIT has been proposed on the basis of the dramatic change of the orbital occupation across the MIT as observed by soft-X-ray absorption spectroscopy measurements.[1]
We present the results of our photoemission investigation of the MIT in VO2 using high quality single crystals and 700eV photon energy. We observe a huge transfer of spectral weight across the MIT and a pronounced two peak structure in the R-phase, supporting recent LDA+DMFT cluster calculations.[2] Similar features are also observed in the insulating phase of the d1-system Ti2O3. The origin of this double peak structure in the insulating phase can be related to the formation of dimers.
[1] M.W. Haverkort et al., Phys. Rev. Lett. 95, 196404 (2005)
[2] S. Biermann et al., Phys. Rev. Lett. 94, 026404 (2005)