Regensburg 1998 – wissenschaftliches Programm

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TT: Tiefe Temperaturen

TT 21: Postersitzung III: Spin-Peierls-Systeme, Metall-Isolator-Übergang, Lokalisierung; SL: Theorie; Quantenflüssigkeiten und -kristalle; Amorphe Materialien, Tunnelsysteme; Borcarbide, Fullerene, konventionelle SL; SL dünner Filme; Experimentiertechniken

TT 21.31: Poster

Donnerstag, 26. März 1998, 15:00–18:30, D

Peierls instability in MoO₂ — •R. Horny¹, V. Eyert², K.-H. Höck¹, and S. R. Horn¹ — ¹Institut für Physik, Universität Augsburg, Memminger Straße 6, D-86135 Augsburg, Germany — ²Hahn-Meitner-Institut, Glienicker Straße 100, D-14109 Berlin, Germany

Molybdenum dioxide crystallizes in a monoclinic structure which deviates only slightly from the rutile structure and which is characteristic of many other dioxides. We present the results of electronic structure calculations for both the monoclinic crystal structure and an assumed rutile structure. The ASW calculations are based on density functional theory within the local density approximation. The results for both crystal structures lay ground for a detailed discussion of the mechanisms favouring the monoclinic structure. The electronic properties of MoO₂ are dominated by O 2p and crystal field splitted Mo 4d states. Chemical stability as analyzed by the crystal orbital overlap population (COOP) results from overlap of these orbitals. Electronic states near the Fermi energy originate almost exclusively from the Mo 4d t_2g states. In particular, the bonding-antibonding splitting of the d_x²−y² orbitals pointing along the rutile c axis signals the role of metal-metal bonding. Investigation of the Fermi surface of the rutile structure reveals a considerable nesting which causes a Peierls instability with a monoclinic lattice and metal-metal pairing both along the rutile c axis and within the basal plane of the rutile structure in agreement with the observed crystal structure of MoO₂ .